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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="cfunction">
<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>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>snprintf(2)</em>.</dd></dl>
<dl class="cfunction">
<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>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>vsnprintf(2)</em>.</dd></dl>
<p><a title="PyOS_snprintf" class="reference internal" href="#PyOS_snprintf"><tt class="xref docutils literal"><span class="pre">PyOS_snprintf()</span></tt></a> and <a title="PyOS_vsnprintf" class="reference internal" href="#PyOS_vsnprintf"><tt class="xref docutils literal"><span class="pre">PyOS_vsnprintf()</span></tt></a> wrap the Standard C library
functions <tt class="xref docutils literal"><span class="pre">snprintf()</span></tt> and <tt class="xref 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 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="cfunction">
<dt id="PyOS_ascii_strtod">
double <tt class="descname">PyOS_ascii_strtod</tt><big>(</big>const char<em> *nptr</em>, char<em> **endptr</em><big>)</big><a class="headerlink" href="#PyOS_ascii_strtod" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert a string to a <tt class="xref docutils literal"><span class="pre">double</span></tt>. This function behaves like the Standard C
function <tt class="xref docutils literal"><span class="pre">strtod()</span></tt> does in the C locale. It does this without changing the
current locale, since that would not be thread-safe.</p>
<p><a title="PyOS_ascii_strtod" class="reference internal" href="#PyOS_ascii_strtod"><tt class="xref docutils literal"><span class="pre">PyOS_ascii_strtod()</span></tt></a> should typically be used for reading configuration
files or other non-user input that should be locale independent.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.4.</span></p>
<p>See the Unix man page <em>strtod(2)</em> for details.</p>
</dd></dl>
<dl class="cfunction">
<dt id="PyOS_ascii_formatd">
char * <tt class="descname">PyOS_ascii_formatd</tt><big>(</big>char<em> *buffer</em>, size_t<em> buf_len</em>, const char<em> *format</em>, double<em> d</em><big>)</big><a class="headerlink" href="#PyOS_ascii_formatd" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert a <tt class="xref docutils literal"><span class="pre">double</span></tt> to a string using the <tt class="docutils literal"><span class="pre">'.'</span></tt> as the decimal
separator. <em>format</em> is a <tt class="xref docutils literal"><span class="pre">printf()</span></tt>-style format string specifying the
number format. Allowed conversion characters are <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> and <tt class="docutils literal"><span class="pre">'G'</span></tt>.</p>
<p>The return value is a pointer to <em>buffer</em> with the converted string or NULL if
the conversion failed.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.4.</span></p>
</dd></dl>
<dl class="cfunction">
<dt id="PyOS_ascii_atof">
double <tt class="descname">PyOS_ascii_atof</tt><big>(</big>const char<em> *nptr</em><big>)</big><a class="headerlink" href="#PyOS_ascii_atof" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert a string to a <tt class="xref docutils literal"><span class="pre">double</span></tt> in a locale-independent way.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.4.</span></p>
<p>See the Unix man page <em>atof(2)</em> for details.</p>
</dd></dl>
<dl class="cfunction">
<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 docutils literal"><span class="pre">strcmp()</span></tt> except that it ignores the case.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
<dl class="cfunction">
<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 docutils literal"><span class="pre">strncmp()</span></tt> except that it ignores the case.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
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