conversion.rst

c

串并转换格式

Functions for number conversion and formatted string output.

:cPyOS_snprintf and :cPyOS_vsnprintf wrap the Standard C library functions :csnprintf and :cvsnprintf. Their purpose is to guarantee consistent behavior in corner cases, which the Standard C functions do not.

The wrappers ensure that str[size-1] is always '\0' upon return. They never write more than size bytes (including the trailing '\0') into str. Both functions require that str != NULL, size > 0 and format != NULL.

If the platform doesn't have :cvsnprintf and the buffer size needed to avoid truncation exceeds size by more than 512 bytes, Python aborts with a Py_FatalError.

The return value (rv) for these functions should be interpreted as follows:

• When 0 <= rv < size, the output conversion was successful and rv characters were written to str (excluding the trailing '\0' byte at str[rv]).
• When rv >= size, the output conversion was truncated and a buffer with rv + 1 bytes would have been needed to succeed. str[size-1] is '\0' in this case.
• When rv < 0, "something bad happened." str[size-1] is '\0' in this case too, but the rest of str is undefined. The exact cause of the error depends on the underlying platform.

The following functions provide locale-independent string to number conversions.