1.. highlightlang:: 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(2)`.
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(2)`.
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`` and ``format !=
31NULL``.
32
33If the platform doesn't have :c:func:`vsnprintf` and the buffer size needed to
34avoid truncation exceeds *size* by more than 512 bytes, Python aborts with a
35*Py_FatalError*.
36
37The return value (*rv*) for these functions should be interpreted as follows:
38
39* When ``0 <= rv < size``, the output conversion was successful and *rv*
40  characters were written to *str* (excluding the trailing ``'\0'`` byte at
41  *str*[*rv*]).
42
43* When ``rv >= size``, the output conversion was truncated and a buffer with
44  ``rv + 1`` bytes would have been needed to succeed. *str*[*size*-1] is ``'\0'``
45  in this case.
46
47* When ``rv < 0``, "something bad happened." *str*[*size*-1] is ``'\0'`` in
48  this case too, but the rest of *str* is undefined. The exact cause of the error
49  depends on the underlying platform.
50
51The following functions provide locale-independent string to number conversions.
52
53
54.. c:function:: double PyOS_string_to_double(const char *s, char **endptr, PyObject *overflow_exception)
55
56   Convert a string ``s`` to a :c:type:`double`, raising a Python
57   exception on failure.  The set of accepted strings corresponds to
58   the set of strings accepted by Python's :func:`float` constructor,
59   except that ``s`` must not have leading or trailing whitespace.
60   The conversion is independent of the current locale.
61
62   If ``endptr`` is ``NULL``, convert the whole string.  Raise
63   ValueError and return ``-1.0`` if the string is not a valid
64   representation of a floating-point number.
65
66   If endptr is not ``NULL``, convert as much of the string as
67   possible and set ``*endptr`` to point to the first unconverted
68   character.  If no initial segment of the string is the valid
69   representation of a floating-point number, set ``*endptr`` to point
70   to the beginning of the string, raise ValueError, and return
71   ``-1.0``.
72
73   If ``s`` represents a value that is too large to store in a float
74   (for example, ``"1e500"`` is such a string on many platforms) then
75   if ``overflow_exception`` is ``NULL`` return ``Py_HUGE_VAL`` (with
76   an appropriate sign) and don't set any exception.  Otherwise,
77   ``overflow_exception`` must point to a Python exception object;
78   raise that exception and return ``-1.0``.  In both cases, set
79   ``*endptr`` to point to the first character after the converted value.
80
81   If any other error occurs during the conversion (for example an
82   out-of-memory error), set the appropriate Python exception and
83   return ``-1.0``.
84
85   .. versionadded:: 2.7
86
87
88.. c:function:: double PyOS_ascii_strtod(const char *nptr, char **endptr)
89
90   Convert a string to a :c:type:`double`. This function behaves like the Standard C
91   function :c:func:`strtod` does in the C locale. It does this without changing the
92   current locale, since that would not be thread-safe.
93
94   :c:func:`PyOS_ascii_strtod` should typically be used for reading configuration
95   files or other non-user input that should be locale independent.
96
97   See the Unix man page :manpage:`strtod(2)` for details.
98
99   .. versionadded:: 2.4
100
101   .. deprecated:: 2.7
102      Use :c:func:`PyOS_string_to_double` instead.
103
104
105
106.. c:function:: char* PyOS_ascii_formatd(char *buffer, size_t buf_len, const char *format, double d)
107
108   Convert a :c:type:`double` to a string using the ``'.'`` as the decimal
109   separator. *format* is a :c:func:`printf`\ -style format string specifying the
110   number format. Allowed conversion characters are ``'e'``, ``'E'``, ``'f'``,
111   ``'F'``, ``'g'`` and ``'G'``.
112
113   The return value is a pointer to *buffer* with the converted string or NULL if
114   the conversion failed.
115
116   .. versionadded:: 2.4
117   .. deprecated:: 2.7
118      This function is removed in Python 2.7 and 3.1.  Use :func:`PyOS_double_to_string`
119      instead.
120
121
122.. c:function:: char* PyOS_double_to_string(double val, char format_code, int precision, int flags, int *ptype)
123
124   Convert a :c:type:`double` *val* to a string using supplied
125   *format_code*, *precision*, and *flags*.
126
127   *format_code* must be one of ``'e'``, ``'E'``, ``'f'``, ``'F'``,
128   ``'g'``, ``'G'`` or ``'r'``.  For ``'r'``, the supplied *precision*
129   must be ``0`` and is ignored.  The ``'r'`` format code specifies the
130   standard :func:`repr` format.
131
132   *flags* can be zero or more of the values *Py_DTSF_SIGN*,
133   *Py_DTSF_ADD_DOT_0*, or *Py_DTSF_ALT*, or-ed together:
134
135   * *Py_DTSF_SIGN* means to always precede the returned string with a sign
136     character, even if *val* is non-negative.
137
138   * *Py_DTSF_ADD_DOT_0* means to ensure that the returned string will not look
139     like an integer.
140
141   * *Py_DTSF_ALT* means to apply "alternate" formatting rules.  See the
142     documentation for the :c:func:`PyOS_snprintf` ``'#'`` specifier for
143     details.
144
145   If *ptype* is non-NULL, then the value it points to will be set to one of
146   *Py_DTST_FINITE*, *Py_DTST_INFINITE*, or *Py_DTST_NAN*, signifying that
147   *val* is a finite number, an infinite number, or not a number, respectively.
148
149   The return value is a pointer to *buffer* with the converted string or
150   *NULL* if the conversion failed. The caller is responsible for freeing the
151   returned string by calling :c:func:`PyMem_Free`.
152
153   .. versionadded:: 2.7
154
155
156.. c:function:: double PyOS_ascii_atof(const char *nptr)
157
158   Convert a string to a :c:type:`double` in a locale-independent way.
159
160   See the Unix man page :manpage:`atof(2)` for details.
161
162   .. versionadded:: 2.4
163
164   .. deprecated:: 3.1
165      Use :c:func:`PyOS_string_to_double` instead.
166
167
168.. c:function:: char* PyOS_stricmp(char *s1, char *s2)
169
170   Case insensitive comparison of strings. The function works almost
171   identically to :c:func:`strcmp` except that it ignores the case.
172
173   .. versionadded:: 2.6
174
175
176.. c:function:: char* PyOS_strnicmp(char *s1, char *s2, Py_ssize_t  size)
177
178   Case insensitive comparison of strings. The function works almost
179   identically to :c:func:`strncmp` except that it ignores the case.
180
181   .. versionadded:: 2.6
182