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<div class="section" id="string-conversion-and-formatting">
<span id="string-conversion"></span><h1>String conversion and formatting<a class="headerlink" href="#string-conversion-and-formatting" title="Permalink to this headline">¶</a></h1>
<p>Functions for number conversion and formatted string output.</p>
<dl class="function">
<dt id="PyOS_snprintf">
int <tt class="descname">PyOS_snprintf</tt><big>(</big>char<em> *str</em>, size_t<em> size</em>, const char<em> *format</em>, ...<big>)</big><a class="headerlink" href="#PyOS_snprintf" title="Permalink to this definition">¶</a></dt>
<dd><p>Output not more than <em>size</em> bytes to <em>str</em> according to the format string
<em>format</em> and the extra arguments. See the Unix man page <em class="manpage">snprintf(2)</em>.</p>
</dd></dl>
<dl class="function">
<dt id="PyOS_vsnprintf">
int <tt class="descname">PyOS_vsnprintf</tt><big>(</big>char<em> *str</em>, size_t<em> size</em>, const char<em> *format</em>, va_list<em> va</em><big>)</big><a class="headerlink" href="#PyOS_vsnprintf" title="Permalink to this definition">¶</a></dt>
<dd><p>Output not more than <em>size</em> bytes to <em>str</em> according to the format string
<em>format</em> and the variable argument list <em>va</em>. Unix man page
<em class="manpage">vsnprintf(2)</em>.</p>
</dd></dl>
<p><a class="reference internal" href="#PyOS_snprintf" title="PyOS_snprintf"><tt class="xref c c-func docutils literal"><span class="pre">PyOS_snprintf()</span></tt></a> and <a class="reference internal" href="#PyOS_vsnprintf" title="PyOS_vsnprintf"><tt class="xref c c-func docutils literal"><span class="pre">PyOS_vsnprintf()</span></tt></a> wrap the Standard C library
functions <tt class="xref c c-func docutils literal"><span class="pre">snprintf()</span></tt> and <tt class="xref c c-func docutils literal"><span class="pre">vsnprintf()</span></tt>. Their purpose is to
guarantee consistent behavior in corner cases, which the Standard C functions do
not.</p>
<p>The wrappers ensure that <em>str*[*size</em>-1] is always <tt class="docutils literal"><span class="pre">'\0'</span></tt> upon return. They
never write more than <em>size</em> bytes (including the trailing <tt class="docutils literal"><span class="pre">'\0'</span></tt>) into str.
Both functions require that <tt class="docutils literal"><span class="pre">str</span> <span class="pre">!=</span> <span class="pre">NULL</span></tt>, <tt class="docutils literal"><span class="pre">size</span> <span class="pre">></span> <span class="pre">0</span></tt> and <tt class="docutils literal"><span class="pre">format</span> <span class="pre">!=</span>
<span class="pre">NULL</span></tt>.</p>
<p>If the platform doesn’t have <tt class="xref c c-func docutils literal"><span class="pre">vsnprintf()</span></tt> and the buffer size needed to
avoid truncation exceeds <em>size</em> by more than 512 bytes, Python aborts with a
<em>Py_FatalError</em>.</p>
<p>The return value (<em>rv</em>) for these functions should be interpreted as follows:</p>
<ul class="simple">
<li>When <tt class="docutils literal"><span class="pre">0</span> <span class="pre"><=</span> <span class="pre">rv</span> <span class="pre"><</span> <span class="pre">size</span></tt>, the output conversion was successful and <em>rv</em>
characters were written to <em>str</em> (excluding the trailing <tt class="docutils literal"><span class="pre">'\0'</span></tt> byte at
<em>str*[*rv</em>]).</li>
<li>When <tt class="docutils literal"><span class="pre">rv</span> <span class="pre">>=</span> <span class="pre">size</span></tt>, the output conversion was truncated and a buffer with
<tt class="docutils literal"><span class="pre">rv</span> <span class="pre">+</span> <span class="pre">1</span></tt> bytes would have been needed to succeed. <em>str*[*size</em>-1] is <tt class="docutils literal"><span class="pre">'\0'</span></tt>
in this case.</li>
<li>When <tt class="docutils literal"><span class="pre">rv</span> <span class="pre"><</span> <span class="pre">0</span></tt>, “something bad happened.” <em>str*[*size</em>-1] is <tt class="docutils literal"><span class="pre">'\0'</span></tt> in
this case too, but the rest of <em>str</em> is undefined. The exact cause of the error
depends on the underlying platform.</li>
</ul>
<p>The following functions provide locale-independent string to number conversions.</p>
<dl class="function">
<dt id="PyOS_string_to_double">
double <tt class="descname">PyOS_string_to_double</tt><big>(</big>const char<em> *s</em>, char<em> **endptr</em>, <a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *overflow_exception</em><big>)</big><a class="headerlink" href="#PyOS_string_to_double" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert a string <tt class="docutils literal"><span class="pre">s</span></tt> to a <tt class="xref c c-type docutils literal"><span class="pre">double</span></tt>, raising a Python
exception on failure. The set of accepted strings corresponds to
the set of strings accepted by Python’s <a class="reference internal" href="../library/functions.html#float" title="float"><tt class="xref py py-func docutils literal"><span class="pre">float()</span></tt></a> constructor,
except that <tt class="docutils literal"><span class="pre">s</span></tt> must not have leading or trailing whitespace.
The conversion is independent of the current locale.</p>
<p>If <tt class="docutils literal"><span class="pre">endptr</span></tt> is <tt class="docutils literal"><span class="pre">NULL</span></tt>, convert the whole string. Raise
ValueError and return <tt class="docutils literal"><span class="pre">-1.0</span></tt> if the string is not a valid
representation of a floating-point number.</p>
<p>If endptr is not <tt class="docutils literal"><span class="pre">NULL</span></tt>, convert as much of the string as
possible and set <tt class="docutils literal"><span class="pre">*endptr</span></tt> to point to the first unconverted
character. If no initial segment of the string is the valid
representation of a floating-point number, set <tt class="docutils literal"><span class="pre">*endptr</span></tt> to point
to the beginning of the string, raise ValueError, and return
<tt class="docutils literal"><span class="pre">-1.0</span></tt>.</p>
<p>If <tt class="docutils literal"><span class="pre">s</span></tt> represents a value that is too large to store in a float
(for example, <tt class="docutils literal"><span class="pre">"1e500"</span></tt> is such a string on many platforms) then
if <tt class="docutils literal"><span class="pre">overflow_exception</span></tt> is <tt class="docutils literal"><span class="pre">NULL</span></tt> return <tt class="docutils literal"><span class="pre">Py_HUGE_VAL</span></tt> (with
an appropriate sign) and don’t set any exception. Otherwise,
<tt class="docutils literal"><span class="pre">overflow_exception</span></tt> must point to a Python exception object;
raise that exception and return <tt class="docutils literal"><span class="pre">-1.0</span></tt>. In both cases, set
<tt class="docutils literal"><span class="pre">*endptr</span></tt> to point to the first character after the converted value.</p>
<p>If any other error occurs during the conversion (for example an
out-of-memory error), set the appropriate Python exception and
return <tt class="docutils literal"><span class="pre">-1.0</span></tt>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.1.</span></p>
</dd></dl>
<dl class="function">
<dt id="PyOS_double_to_string">
char* <tt class="descname">PyOS_double_to_string</tt><big>(</big>double<em> val</em>, char<em> format_code</em>, int<em> precision</em>, int<em> flags</em>, int<em> *ptype</em><big>)</big><a class="headerlink" href="#PyOS_double_to_string" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert a <tt class="xref c c-type docutils literal"><span class="pre">double</span></tt> <em>val</em> to a string using supplied
<em>format_code</em>, <em>precision</em>, and <em>flags</em>.</p>
<p><em>format_code</em> must be one of <tt class="docutils literal"><span class="pre">'e'</span></tt>, <tt class="docutils literal"><span class="pre">'E'</span></tt>, <tt class="docutils literal"><span class="pre">'f'</span></tt>, <tt class="docutils literal"><span class="pre">'F'</span></tt>,
<tt class="docutils literal"><span class="pre">'g'</span></tt>, <tt class="docutils literal"><span class="pre">'G'</span></tt> or <tt class="docutils literal"><span class="pre">'r'</span></tt>. For <tt class="docutils literal"><span class="pre">'r'</span></tt>, the supplied <em>precision</em>
must be 0 and is ignored. The <tt class="docutils literal"><span class="pre">'r'</span></tt> format code specifies the
standard <a class="reference internal" href="../library/functions.html#repr" title="repr"><tt class="xref py py-func docutils literal"><span class="pre">repr()</span></tt></a> format.</p>
<p><em>flags</em> can be zero or more of the values <em>Py_DTSF_SIGN</em>,
<em>Py_DTSF_ADD_DOT_0</em>, or <em>Py_DTSF_ALT</em>, or-ed together:</p>
<ul class="simple">
<li><em>Py_DTSF_SIGN</em> means to always precede the returned string with a sign
character, even if <em>val</em> is non-negative.</li>
<li><em>Py_DTSF_ADD_DOT_0</em> means to ensure that the returned string will not look
like an integer.</li>
<li><em>Py_DTSF_ALT</em> means to apply “alternate” formatting rules. See the
documentation for the <a class="reference internal" href="#PyOS_snprintf" title="PyOS_snprintf"><tt class="xref c c-func docutils literal"><span class="pre">PyOS_snprintf()</span></tt></a> <tt class="docutils literal"><span class="pre">'#'</span></tt> specifier for
details.</li>
</ul>
<p>If <em>ptype</em> is non-NULL, then the value it points to will be set to one of
<em>Py_DTST_FINITE</em>, <em>Py_DTST_INFINITE</em>, or <em>Py_DTST_NAN</em>, signifying that
<em>val</em> is a finite number, an infinite number, or not a number, respectively.</p>
<p>The return value is a pointer to <em>buffer</em> with the converted string or
<em>NULL</em> if the conversion failed. The caller is responsible for freeing the
returned string by calling <a class="reference internal" href="memory.html#PyMem_Free" title="PyMem_Free"><tt class="xref c c-func docutils literal"><span class="pre">PyMem_Free()</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.1.</span></p>
</dd></dl>
<dl class="function">
<dt id="PyOS_stricmp">
char* <tt class="descname">PyOS_stricmp</tt><big>(</big>char<em> *s1</em>, char<em> *s2</em><big>)</big><a class="headerlink" href="#PyOS_stricmp" title="Permalink to this definition">¶</a></dt>
<dd><p>Case insensitive comparison of strings. The function works almost
identically to <tt class="xref c c-func docutils literal"><span class="pre">strcmp()</span></tt> except that it ignores the case.</p>
</dd></dl>
<dl class="function">
<dt id="PyOS_strnicmp">
char* <tt class="descname">PyOS_strnicmp</tt><big>(</big>char<em> *s1</em>, char<em> *s2</em>, Py_ssize_t <em> size</em><big>)</big><a class="headerlink" href="#PyOS_strnicmp" title="Permalink to this definition">¶</a></dt>
<dd><p>Case insensitive comparison of strings. The function works almost
identically to <tt class="xref c c-func docutils literal"><span class="pre">strncmp()</span></tt> except that it ignores the case.</p>
</dd></dl>
</div>
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