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// Copyright 2013 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_STRINGS_SAFE_SPRINTF_H_
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#define BASE_STRINGS_SAFE_SPRINTF_H_
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#include "build/build_config.h"
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#include "base/base_export.h"
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#include "base/basictypes.h"
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// Define ssize_t inside of our namespace.
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typedef __int64 ssize_t;
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// SafeSPrintf() is a type-safe and completely self-contained version of
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// SafeSNPrintf() is an alternative function signature that can be used when
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// not dealing with fixed-sized buffers. When possible, SafeSPrintf() should
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// always be used instead of SafeSNPrintf()
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// These functions allow for formatting complicated messages from contexts that
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// require strict async-signal-safety. In fact, it is safe to call them from
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// any low-level execution context, as they are guaranteed to make no library
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// or system calls. It deliberately never touches "errno", either.
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// The only exception to this rule is that in debug builds the code calls
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// RAW_CHECK() to help diagnose problems when the format string does not
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// match the rest of the arguments. In release builds, no CHECK()s are used,
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// and SafeSPrintf() instead returns an output string that expands only
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// those arguments that match their format characters. Mismatched arguments
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// The code currently only supports a subset of format characters:
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// %c, %o, %d, %x, %X, %p, and %s.
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// SafeSPrintf() aims to be as liberal as reasonably possible. Integer-like
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// values of arbitrary width can be passed to all of the format characters
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// that expect integers. Thus, it is explicitly legal to pass an "int" to
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// "%c", and output will automatically look at the LSB only. It is also
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// explicitly legal to pass either signed or unsigned values, and the format
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// characters will automatically interpret the arguments accordingly.
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// It is still not legal to mix-and-match integer-like values with pointer
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// values. For instance, you cannot pass a pointer to %x, nor can you pass an
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// The one exception is "0" zero being accepted by "%p". This works-around
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// the problem of C++ defining NULL as an integer-like value.
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// All format characters take an optional width parameter. This must be a
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// positive integer. For %d, %o, %x, %X and %p, if the width starts with
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// a leading '0', padding is done with '0' instead of ' ' characters.
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// There are a few features of snprintf()-style format strings, that
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// SafeSPrintf() does not support at this time.
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// If an actual user showed up, there is no particularly strong reason they
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// couldn't be added. But that assumes that the trade-offs between complexity
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// and utility are favorable.
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// For example, adding support for negative padding widths, and for %n are all
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// likely to be viewed positively. They are all clearly useful, low-risk, easy
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// to test, don't jeopardize the async-signal-safety of the code, and overall
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// have little impact on other parts of SafeSPrintf() function.
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// On the other hands, adding support for alternate forms, positional
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// arguments, grouping, wide characters, localization or floating point numbers
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// are all unlikely to ever be added.
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// SafeSPrintf() and SafeSNPrintf() mimic the behavior of snprintf() and they
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// return the number of bytes needed to store the untruncated output. This
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// does *not* include the terminating NUL byte.
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// They return -1, iff a fatal error happened. This typically can only happen,
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// if the buffer size is a) negative, or b) zero (i.e. not even the NUL byte
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// can be written). The return value can never be larger than SSIZE_MAX-1.
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// This ensures that the caller can always add one to the signed return code
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// in order to determine the amount of storage that needs to be allocated.
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// While the code supports type checking and while it is generally very careful
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// to avoid printing incorrect values, it tends to be conservative in printing
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// as much as possible, even when given incorrect parameters. Typically, in
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// case of an error, the format string will not be expanded. (i.e. something
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// like SafeSPrintf(buf, "%p %d", 1, 2) results in "%p 2"). See above for
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// the use of RAW_CHECK() in debug builds, though.
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// base::strings::SafeSPrintf(buf, "The answer: %2d", 42);
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// Example with dynamically sized buffer (async-signal-safe). This code won't
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// work on Visual studio, as it requires dynamically allocating arrays on the
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// stack. Consider picking a smaller value for |kMaxSize| if stack size is
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// limited and known. On the other hand, if the parameters to SafeSNPrintf()
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// are trusted and not controllable by the user, you can consider eliminating
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// the check for |kMaxSize| altogether. The current value of SSIZE_MAX is
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// essentially a no-op that just illustrates how to implement an upper bound:
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// const size_t kInitialSize = 128;
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// const size_t kMaxSize = std::numeric_limits<ssize_t>::max();
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// size_t size = kInitialSize;
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// size = SafeSNPrintf(buf, size, "Error message \"%s\"\n", err) + 1;
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// if (sizeof(buf) < kMaxSize && size > kMaxSize) {
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// } else if (size > sizeof(buf))
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// write(2, buf, size-1);
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// Helpers that use C++ overloading, templates, and specializations to deduce
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// and record type information from function arguments. This allows us to
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// later write a type-safe version of snprintf().
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enum Type { INT, UINT, STRING, POINTER };
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// Any integer-like value.
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Arg(signed char c) : i(c), width(sizeof(char)), type(INT) { }
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Arg(unsigned char c) : i(c), width(sizeof(char)), type(UINT) { }
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Arg(signed short j) : i(j), width(sizeof(short)), type(INT) { }
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Arg(unsigned short j) : i(j), width(sizeof(short)), type(UINT) { }
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Arg(signed int j) : i(j), width(sizeof(int)), type(INT) { }
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Arg(unsigned int j) : i(j), width(sizeof(int)), type(UINT) { }
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Arg(signed long j) : i(j), width(sizeof(long)), type(INT) { }
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Arg(unsigned long j) : i(j), width(sizeof(long)), type(UINT) { }
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Arg(signed long long j) : i(j), width(sizeof(long long)), type(INT) { }
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Arg(unsigned long long j) : i(j), width(sizeof(long long)), type(UINT) { }
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// A C-style text string.
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Arg(const char* s) : str(s), type(STRING) { }
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Arg(char* s) : str(s), type(STRING) { }
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// Any pointer value that can be cast to a "void*".
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template<class T> Arg(T* p) : ptr((void*)p), type(POINTER) { }
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// An integer-like value.
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// A C-style text string.
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// A pointer to an arbitrary object.
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const enum Type type;
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// This is the internal function that performs the actual formatting of
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// an snprintf()-style format string.
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BASE_EXPORT ssize_t SafeSNPrintf(char* buf, size_t sz, const char* fmt,
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const Arg* args, size_t max_args);
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// In debug builds, allow unit tests to artificially lower the kSSizeMax
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// constant that is used as a hard upper-bound for all buffers. In normal
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// use, this constant should always be std::numeric_limits<ssize_t>::max().
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BASE_EXPORT void SetSafeSPrintfSSizeMaxForTest(size_t max);
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BASE_EXPORT size_t GetSafeSPrintfSSizeMaxForTest();
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} // namespace internal
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// TODO(markus): C++11 has a much more concise and readable solution for
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// expressing what we are doing here.
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template<class T0, class T1, class T2, class T3, class T4,
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class T5, class T6, class T7, class T8, class T9>
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4,
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T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = {
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arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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class T0, class T1, class T2, class T3, class T4,
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class T5, class T6, class T7, class T8, class T9>
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4,
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T5 arg5, T6 arg6, T7 arg7, T8 arg8, T9 arg9) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = {
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arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<class T0, class T1, class T2, class T3, class T4,
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class T5, class T6, class T7, class T8>
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4,
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T5 arg5, T6 arg6, T7 arg7, T8 arg8) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = {
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arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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class T0, class T1, class T2, class T3, class T4, class T5,
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class T6, class T7, class T8>
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4,
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T5 arg5, T6 arg6, T7 arg7, T8 arg8) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = {
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arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<class T0, class T1, class T2, class T3, class T4, class T5,
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4,
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T5 arg5, T6 arg6, T7 arg7) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = {
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arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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class T0, class T1, class T2, class T3, class T4, class T5,
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4,
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T5 arg5, T6 arg6, T7 arg7) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = {
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arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<class T0, class T1, class T2, class T3, class T4, class T5,
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4,
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = {
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arg0, arg1, arg2, arg3, arg4, arg5, arg6
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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class T0, class T1, class T2, class T3, class T4, class T5,
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5,
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = {
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arg0, arg1, arg2, arg3, arg4, arg5, arg6
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<class T0, class T1, class T2, class T3, class T4, class T5>
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1, arg2, arg3, arg4, arg5 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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class T0, class T1, class T2, class T3, class T4, class T5>
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1, arg2, arg3, arg4, arg5 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<class T0, class T1, class T2, class T3, class T4>
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1, arg2, arg3, arg4 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<size_t N, class T0, class T1, class T2, class T3, class T4>
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt, T0 arg0, T1 arg1,
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T2 arg2, T3 arg3, T4 arg4) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1, arg2, arg3, arg4 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<class T0, class T1, class T2, class T3>
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1, arg2, arg3 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<size_t N, class T0, class T1, class T2, class T3>
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt,
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T0 arg0, T1 arg1, T2 arg2, T3 arg3) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1, arg2, arg3 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<class T0, class T1, class T2>
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt,
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T0 arg0, T1 arg1, T2 arg2) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1, arg2 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<size_t N, class T0, class T1, class T2>
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt, T0 arg0, T1 arg1,
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1, arg2 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<class T0, class T1>
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt, T0 arg0, T1 arg1) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<size_t N, class T0, class T1>
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt, T0 arg0, T1 arg1) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0, arg1 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt, T0 arg0) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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template<size_t N, class T0>
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ssize_t SafeSPrintf(char (&buf)[N], const char* fmt, T0 arg0) {
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// Use Arg() object to record type information and then copy arguments to an
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// array to make it easier to iterate over them.
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const internal::Arg arg_array[] = { arg0 };
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return internal::SafeSNPrintf(buf, N, fmt, arg_array, arraysize(arg_array));
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// Fast-path when we don't actually need to substitute any arguments.
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BASE_EXPORT ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt);
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inline ssize_t SafeSPrintf(char (&buf)[N], const char* fmt) {
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return SafeSNPrintf(buf, N, fmt);
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} // namespace strings
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#endif // BASE_STRINGS_SAFE_SPRINTF_H_