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Add a warning message about PyOS_snprintf (#95993)

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Eric Wieser 2022-10-07 11:49:53 -07:00 committed by GitHub
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3
Doc/c-api/conversion.rst
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@ -28,7 +28,8 @@ not.
The wrappers ensure that ``str[size-1]`` is always ``'\0'`` upon return. They 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. never write more than *size* bytes (including the trailing ``'\0'``) into str.
Both functions require that ``str != NULL``, ``size > 0``, ``format != NULL`` Both functions require that ``str != NULL``, ``size > 0``, ``format != NULL``
and ``size < INT_MAX``. and ``size < INT_MAX``. Note that this means there is no equivalent to the C99
``n = snprintf(NULL, 0, ...)`` which would determine the necessary buffer size.
The return value (*rv*) for these functions should be interpreted as follows: The return value (*rv*) for these functions should be interpreted as follows:

1
Python/mysnprintf.c
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@ -9,6 +9,7 @@
would have been written had the buffer not been too small, and to set would have been written had the buffer not been too small, and to set
the last byte of the buffer to \0. At least MS _vsnprintf returns a the last byte of the buffer to \0. At least MS _vsnprintf returns a
negative value instead, and fills the entire buffer with non-\0 data. negative value instead, and fills the entire buffer with non-\0 data.
Unlike C99, our wrappers do not support passing a null buffer.
The wrappers ensure that str[size-1] is always \0 upon return. The wrappers ensure that str[size-1] is always \0 upon return.