void StringAppendVT(const CharType *format, va_list ap, std::basic_string<CharType> &output)
{
CharType stack_buffer[1024];
/* first, we try to finish the task using a fixed-size buffer in the stack */
va_list ap_copy;
GG_VA_COPY(ap_copy, ap);
int result = vsnprintfT(stack_buffer, COUNT_OF(stack_buffer), format, ap_copy);
va_end(ap_copy);
if (result >= 0 && result < static_cast<int>(COUNT_OF(stack_buffer)))
{
/* It fits */
output.append(stack_buffer, result);
return;
}
/* then, we have to repeatedly increase buffer size until it fits. */
int buffer_size = COUNT_OF(stack_buffer);
std::basic_string<CharType> heap_buffer;
for (;;)
{
if (result != -1)
{
assert(0);
return; /* not expected, result should be -1 here */
}
buffer_size <<= 1; /* try doubling the buffer size */
if (buffer_size > 32 * 1024 * 1024)
{
assert(0);
return; /* too long */
}
/* resize */
heap_buffer.resize(buffer_size);
/*
* NOTE: You can only use a va_list once. Since we're in a while loop, we
* need to make a new copy each time so we don't use up the original.
*/
GG_VA_COPY(ap_copy, ap);
result = vsnprintfT(&heap_buffer[0], buffer_size, format, ap_copy);
va_end(ap_copy);
if ((result >= 0) && (result < buffer_size)) {
/* It fits */
output.append(&heap_buffer[0], result);
return;
}
}
}
void StringAppendFT(strT* str, const typename strT::value_type* fmt, va_list ap)
{
typedef typename strT::value_type charT;
const int kDefaultCharCount = 1024;
charT buf[kDefaultCharCount];
int ret = vsnprintfT(buf, kDefaultCharCount, kDefaultCharCount - 1, fmt, ap);
if (ret >= 0) {
str->append(buf, ret);
return;
}
// data is truncated.
// adjust the buffer size until it fits
const int kMaxAllowedCharCount = (1 << 25);
int tentative_char_count = kDefaultCharCount;
while (true) {
tentative_char_count <<= 1;
if (tentative_char_count > kMaxAllowedCharCount) {
throw StringFormatDataLengthError("memory needed exceeds the maximum value");
}
std::vector<charT> dynamic_buf(tentative_char_count);
// vsnprintf-like functions on Windows don't change the |ap|
// while their counterparts on Linux do.
// if you use VS2013 or higher, or compilers that support C99
// you alternatively can use |va_copy| to make a copy of |ap|
// during each iteration.
int ret = vsnprintfT(&dynamic_buf[0], tentative_char_count,
tentative_char_count - 1, fmt, ap);
if (ret >= 0) {
str->append(&dynamic_buf[0], ret);
return;
}
}
}
