1#include "Python.h" 2 3/* snprintf() and vsnprintf() wrappers. 4 5 If the platform has vsnprintf, we use it, else we 6 emulate it in a half-hearted way. Even if the platform has it, we wrap 7 it because platforms differ in what vsnprintf does in case the buffer 8 is too small: C99 behavior is to return the number of characters that 9 would have been written had the buffer not been too small, and to set 10 the last byte of the buffer to \0. At least MS _vsnprintf returns a 11 negative value instead, and fills the entire buffer with non-\0 data. 12 Unlike C99, our wrappers do not support passing a null buffer. 13 14 The wrappers ensure that str[size-1] is always \0 upon return. 15 16 PyOS_snprintf and PyOS_vsnprintf never write more than size bytes 17 (including the trailing '\0') into str. 18 19 Return value (rv): 20 21 When 0 <= rv < size, the output conversion was unexceptional, and 22 rv characters were written to str (excluding a trailing \0 byte at 23 str[rv]). 24 25 When rv >= size, output conversion was truncated, and a buffer of 26 size rv+1 would have been needed to avoid truncation. str[size-1] 27 is \0 in this case. 28 29 When rv < 0, "something bad happened". str[size-1] is \0 in this 30 case too, but the rest of str is unreliable. It could be that 31 an error in format codes was detected by libc, or on platforms 32 with a non-C99 vsnprintf simply that the buffer wasn't big enough 33 to avoid truncation, or on platforms without any vsnprintf that 34 PyMem_Malloc couldn't obtain space for a temp buffer. 35 36 CAUTION: Unlike C99, str != NULL and size > 0 are required. 37 Also, size must be smaller than INT_MAX. 38*/ 39 40int 41PyOS_snprintf(char *str, size_t size, const char *format, ...) 42{ 43 int rc; 44 va_list va; 45 46 va_start(va, format); 47 rc = PyOS_vsnprintf(str, size, format, va); 48 va_end(va); 49 return rc; 50} 51 52int 53PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va) 54{ 55 assert(str != NULL); 56 assert(size > 0); 57 assert(size <= (INT_MAX - 1)); 58 assert(format != NULL); 59 60 int len; /* # bytes written, excluding \0 */ 61 /* We take a size_t as input but return an int. Sanity check 62 * our input so that it won't cause an overflow in the 63 * vsnprintf return value. */ 64 if (size > INT_MAX - 1) { 65 len = -666; 66 goto Done; 67 } 68 69#if defined(_MSC_VER) 70 len = _vsnprintf(str, size, format, va); 71#else 72 len = vsnprintf(str, size, format, va); 73#endif 74 75Done: 76 if (size > 0) { 77 str[size-1] = '\0'; 78 } 79 return len; 80} 81