src/stringprintf.cc

// Copyright 2011 Google Inc. All Rights Reserved.
// Author: enh@google.com (Elliott Hughes)

#include "stringprintf.h"

#include <stdio.h>

void StringAppendV(std::string* dst, const char* format, va_list ap) {
  // First try with a small fixed size buffer
  char space[1024];

  // It's possible for methods that use a va_list to invalidate
  // the data in it upon use.  The fix is to make a copy
  // of the structure before using it and use that copy instead.
  va_list backup_ap;
  va_copy(backup_ap, ap);
  int result = vsnprintf(space, sizeof(space), format, backup_ap);
  va_end(backup_ap);

  if (result < int(sizeof(space))) {
    if (result >= 0) {
      // Normal case -- everything fit.
      dst->append(space, result);
      return;
    }

    if (result < 0) {
      // Just an error.
      return;
    }
  }

  // Increase the buffer size to the size requested by vsnprintf,
  // plus one for the closing \0.
  int length = result+1;
  char* buf = new char[length];

  // Restore the va_list before we use it again
  va_copy(backup_ap, ap);
  result = vsnprintf(buf, length, format, backup_ap);
  va_end(backup_ap);

  if (result >= 0 && result < length) {
    // It fit
    dst->append(buf, result);
  }
  delete[] buf;
}

std::string StringPrintf(const char* fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  std::string result;
  StringAppendV(&result, fmt, ap);
  va_end(ap);
  return result;
}

void StringAppendF(std::string* dst, const char* format, ...) {
  va_list ap;
  va_start(ap, format);
  StringAppendV(dst, format, ap);
  va_end(ap);
}