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//===- Format.h - Efficient printf-style formatting for streams -*- C++ -*-===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This file implements the format() function, which can be used with other
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// LLVM subsystems to provide printf-style formatting. This gives all the power
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// and risk of printf. This can be used like this (with raw_ostreams as an
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// OS << "mynumber: " << format("%4.5f", 1234.412) << '\n';
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// OS << format("mynumber: %4.5f\n", 1234.412);
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_FORMAT_H
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#define LLVM_SUPPORT_FORMAT_H
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// FIXME: This define is wrong:
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// - _snprintf does not guarantee that trailing null is always added - if
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// there is no space for null, it does not report any error.
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// - According to C++ standard, snprintf should be visible in the 'std'
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// namespace - this define makes this impossible.
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#define snprintf _snprintf
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/// format_object_base - This is a helper class used for handling formatted
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/// output. It is the abstract base class of a templated derived class.
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class format_object_base {
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virtual void home(); // Out of line virtual method.
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/// snprint - Call snprintf() for this object, on the given buffer and size.
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virtual int snprint(char *Buffer, unsigned BufferSize) const = 0;
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format_object_base(const char *fmt) : Fmt(fmt) {}
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virtual ~format_object_base() {}
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/// print - Format the object into the specified buffer. On success, this
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/// returns the length of the formatted string. If the buffer is too small,
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/// this returns a length to retry with, which will be larger than BufferSize.
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unsigned print(char *Buffer, unsigned BufferSize) const {
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assert(BufferSize && "Invalid buffer size!");
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// Print the string, leaving room for the terminating null.
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int N = snprint(Buffer, BufferSize);
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// VC++ and old GlibC return negative on overflow, just double the size.
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// Other impls yield number of bytes needed, not including the final '\0'.
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if (unsigned(N) >= BufferSize)
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// Otherwise N is the length of output (not including the final '\0').
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/// format_object1 - This is a templated helper class used by the format
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/// function that captures the object to be formated and the format string. When
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/// actually printed, this synthesizes the string into a temporary buffer
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/// provided and returns whether or not it is big enough.
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class format_object1 : public format_object_base {
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format_object1(const char *fmt, const T &val)
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: format_object_base(fmt), Val(val) {
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virtual int snprint(char *Buffer, unsigned BufferSize) const {
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return snprintf(Buffer, BufferSize, Fmt, Val);
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/// format_object2 - This is a templated helper class used by the format
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/// function that captures the object to be formated and the format string. When
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/// actually printed, this synthesizes the string into a temporary buffer
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/// provided and returns whether or not it is big enough.
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template <typename T1, typename T2>
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class format_object2 : public format_object_base {
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format_object2(const char *fmt, const T1 &val1, const T2 &val2)
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: format_object_base(fmt), Val1(val1), Val2(val2) {
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virtual int snprint(char *Buffer, unsigned BufferSize) const {
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return snprintf(Buffer, BufferSize, Fmt, Val1, Val2);
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/// format_object3 - This is a templated helper class used by the format
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/// function that captures the object to be formated and the format string. When
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/// actually printed, this synthesizes the string into a temporary buffer
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/// provided and returns whether or not it is big enough.
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template <typename T1, typename T2, typename T3>
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class format_object3 : public format_object_base {
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format_object3(const char *fmt, const T1 &val1, const T2 &val2,const T3 &val3)
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: format_object_base(fmt), Val1(val1), Val2(val2), Val3(val3) {
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virtual int snprint(char *Buffer, unsigned BufferSize) const {
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return snprintf(Buffer, BufferSize, Fmt, Val1, Val2, Val3);
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/// format - This is a helper function that is used to produce formatted output.
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/// This is typically used like: OS << format("%0.4f", myfloat) << '\n';
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template <typename T>
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inline format_object1<T> format(const char *Fmt, const T &Val) {
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return format_object1<T>(Fmt, Val);
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/// format - This is a helper function that is used to produce formatted output.
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/// This is typically used like: OS << format("%0.4f", myfloat) << '\n';
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template <typename T1, typename T2>
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inline format_object2<T1, T2> format(const char *Fmt, const T1 &Val1,
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return format_object2<T1, T2>(Fmt, Val1, Val2);
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/// format - This is a helper function that is used to produce formatted output.
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/// This is typically used like: OS << format("%0.4f", myfloat) << '\n';
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template <typename T1, typename T2, typename T3>
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inline format_object3<T1, T2, T3> format(const char *Fmt, const T1 &Val1,
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const T2 &Val2, const T3 &Val3) {
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return format_object3<T1, T2, T3>(Fmt, Val1, Val2, Val3);
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} // end namespace llvm