1.. highlight:: c
2
3.. _string-conversion:
4
5String conversion and formatting
6================================
7
8Functions for number conversion and formatted string output.
9
10
11.. c:function:: int PyOS_snprintf(char *str, size_t size,  const char *format, ...)
12
13   Output not more than *size* bytes to *str* according to the format string
14   *format* and the extra arguments. See the Unix man page :manpage:`snprintf(3)`.
15
16
17.. c:function:: int PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
18
19   Output not more than *size* bytes to *str* according to the format string
20   *format* and the variable argument list *va*. Unix man page
21   :manpage:`vsnprintf(3)`.
22
23:c:func:`PyOS_snprintf` and :c:func:`PyOS_vsnprintf` wrap the Standard C library
24functions :c:func:`snprintf` and :c:func:`vsnprintf`. Their purpose is to
25guarantee consistent behavior in corner cases, which the Standard C functions do
26not.
27
28The wrappers ensure that ``str[size-1]`` is always ``'\0'`` upon return. They
29never write more than *size* bytes (including the trailing ``'\0'``) into str.
30Both functions require that ``str != NULL``, ``size > 0``, ``format != NULL``
31and ``size < INT_MAX``. Note that this means there is no equivalent to the C99
32``n = snprintf(NULL, 0, ...)`` which would determine the necessary buffer size.
33
34The return value (*rv*) for these functions should be interpreted as follows:
35
36* When ``0 <= rv < size``, the output conversion was successful and *rv*
37  characters were written to *str* (excluding the trailing ``'\0'`` byte at
38  ``str[rv]``).
39
40* When ``rv >= size``, the output conversion was truncated and a buffer with
41  ``rv + 1`` bytes would have been needed to succeed. ``str[size-1]`` is ``'\0'``
42  in this case.
43
44* When ``rv < 0``, "something bad happened." ``str[size-1]`` is ``'\0'`` in
45  this case too, but the rest of *str* is undefined. The exact cause of the error
46  depends on the underlying platform.
47
48
49The following functions provide locale-independent string to number conversions.
50
51.. c:function:: double PyOS_string_to_double(const char *s, char **endptr, PyObject *overflow_exception)
52
53   Convert a string ``s`` to a :c:expr:`double`, raising a Python
54   exception on failure.  The set of accepted strings corresponds to
55   the set of strings accepted by Python's :func:`float` constructor,
56   except that ``s`` must not have leading or trailing whitespace.
57   The conversion is independent of the current locale.
58
59   If ``endptr`` is ``NULL``, convert the whole string.  Raise
60   :exc:`ValueError` and return ``-1.0`` if the string is not a valid
61   representation of a floating-point number.
62
63   If endptr is not ``NULL``, convert as much of the string as
64   possible and set ``*endptr`` to point to the first unconverted
65   character.  If no initial segment of the string is the valid
66   representation of a floating-point number, set ``*endptr`` to point
67   to the beginning of the string, raise ValueError, and return
68   ``-1.0``.
69
70   If ``s`` represents a value that is too large to store in a float
71   (for example, ``"1e500"`` is such a string on many platforms) then
72   if ``overflow_exception`` is ``NULL`` return ``Py_HUGE_VAL`` (with
73   an appropriate sign) and don't set any exception.  Otherwise,
74   ``overflow_exception`` must point to a Python exception object;
75   raise that exception and return ``-1.0``.  In both cases, set
76   ``*endptr`` to point to the first character after the converted value.
77
78   If any other error occurs during the conversion (for example an
79   out-of-memory error), set the appropriate Python exception and
80   return ``-1.0``.
81
82   .. versionadded:: 3.1
83
84
85.. c:function:: char* PyOS_double_to_string(double val, char format_code, int precision, int flags, int *ptype)
86
87   Convert a :c:expr:`double` *val* to a string using supplied
88   *format_code*, *precision*, and *flags*.
89
90   *format_code* must be one of ``'e'``, ``'E'``, ``'f'``, ``'F'``,
91   ``'g'``, ``'G'`` or ``'r'``.  For ``'r'``, the supplied *precision*
92   must be 0 and is ignored.  The ``'r'`` format code specifies the
93   standard :func:`repr` format.
94
95   *flags* can be zero or more of the values ``Py_DTSF_SIGN``,
96   ``Py_DTSF_ADD_DOT_0``, or ``Py_DTSF_ALT``, or-ed together:
97
98   * ``Py_DTSF_SIGN`` means to always precede the returned string with a sign
99     character, even if *val* is non-negative.
100
101   * ``Py_DTSF_ADD_DOT_0`` means to ensure that the returned string will not look
102     like an integer.
103
104   * ``Py_DTSF_ALT`` means to apply "alternate" formatting rules.  See the
105     documentation for the :c:func:`PyOS_snprintf` ``'#'`` specifier for
106     details.
107
108   If *ptype* is non-``NULL``, then the value it points to will be set to one of
109   ``Py_DTST_FINITE``, ``Py_DTST_INFINITE``, or ``Py_DTST_NAN``, signifying that
110   *val* is a finite number, an infinite number, or not a number, respectively.
111
112   The return value is a pointer to *buffer* with the converted string or
113   ``NULL`` if the conversion failed. The caller is responsible for freeing the
114   returned string by calling :c:func:`PyMem_Free`.
115
116   .. versionadded:: 3.1
117
118
119.. c:function:: int PyOS_stricmp(const char *s1, const char *s2)
120
121   Case insensitive comparison of strings. The function works almost
122   identically to :c:func:`strcmp` except that it ignores the case.
123
124
125.. c:function:: int PyOS_strnicmp(const char *s1, const char *s2, Py_ssize_t  size)
126
127   Case insensitive comparison of strings. The function works almost
128   identically to :c:func:`strncmp` except that it ignores the case.
129