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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>fscanf</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="fscanf"></a> <a name="tag_03_190"></a><!-- fscanf --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_190_01"></a>NAME</h4><blockquote>fscanf, scanf, sscanf - convert formatted input</blockquote><h4><a name="tag_03_190_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/stdio.h.html">stdio.h</a>><br><br> int fscanf(FILE *restrict</tt> <i>stream</i><tt>, const char *restrict</tt> <i>format</i><tt>, ... );<br> int scanf(const char *restrict</tt> <i>format</i><tt>, ... );<br> int sscanf(const char *restrict</tt> <i>s</i><tt>, const char *restrict</tt> <i>format</i><tt>, ... );<br></tt></code></p></blockquote><h4><a name="tag_03_190_03"></a>DESCRIPTION</h4><blockquote><div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between therequirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers tothe ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div><p>The <i>fscanf</i>() function shall read from the named input <i>stream</i>. The <i>scanf</i>() function shall read from thestandard input stream <i>stdin</i>. The <i>sscanf</i>() function shall read from the string <i>s</i>. Each function reads bytes,interprets them according to a format, and stores the results in its arguments. Each expects, as arguments, a control string<i>format</i> described below, and a set of <i>pointer</i> arguments indicating where the converted input should be stored. Theresult is undefined if there are insufficient arguments for the format. If the format is exhausted while arguments remain, theexcess arguments shall be evaluated but otherwise ignored.</p><p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Conversions can be applied to the <i>n</i>th argument after the <i>format</i> in the argument list, rather than to the next unusedargument. In this case, the conversion specifier character <tt>%</tt> (see below) is replaced by the sequence<tt>"%</tt><i>n</i><tt>$"</tt>, where <i>n</i> is a decimal integer in the range [1,{NL_ARGMAX}]. This feature provides for thedefinition of format strings that select arguments in an order appropriate to specific languages. In format strings containing the<tt>"%</tt><i>n</i><tt>$"</tt> form of conversion specifications, it is unspecified whether numbered arguments in the argument listcan be referenced from the format string more than once.</p><p>The <i>format</i> can contain either form of a conversion specification-that is, <tt>%</tt> or<tt>"%</tt><i>n</i><tt>$"</tt>-but the two forms cannot be mixed within a single <i>format</i> string. The only exception to thisis that <tt>%%</tt> or <tt>%*</tt> can be mixed with the <tt>"%</tt><i>n</i><tt>$"</tt> form. When numbered argument specificationsare used, specifying the <i>N</i>th argument requires that all the leading arguments, from the first to the ( <i>N</i>-1)th, arepointers. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p><p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The<i>fscanf</i>() function in all its forms shall allow detection of a language-dependent radix character in the input string. Theradix character is defined in the program's locale (category <i>LC_NUMERIC ).</i> In the POSIX locale, or in a locale where theradix character is not defined, the radix character shall default to a period ( <tt>'.'</tt> ). <img src="../images/opt-end.gif"alt="[Option End]" border="0"></p><p>The format is a character string, beginning and ending in its initial shift state, if any, composed of zero or more directives.Each directive is composed of one of the following: one or more white-space characters ( <space>s, <tab>s,<newline>s, <vertical-tab>s, or <form-feed>s); an ordinary character (neither <tt>'%'</tt> nor a white-spacecharacter); or a conversion specification. Each conversion specification is introduced by the character <tt>'%'</tt> <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> or thecharacter sequence <tt>"%</tt><i>n</i><tt>$"</tt>, <img src="../images/opt-end.gif" alt="[Option End]" border="0"> afterwhich the following appear in sequence:</p><ul><li><p>An optional assignment-suppressing character <tt>'*'</tt> .</p></li><li><p>An optional non-zero decimal integer that specifies the maximum field width.</p></li><li><p>An option length modifier that specifies the size of the receiving object.</p></li><li><p>A <i>conversion specifier</i> character that specifies the type of conversion to be applied. The valid conversion specifiers aredescribed below.</p></li></ul><p>The <i>fscanf</i>() functions shall execute each directive of the format in turn. If a directive fails, as detailed below, thefunction shall return. Failures are described as input failures (due to the unavailability of input bytes) or matching failures(due to inappropriate input).</p><p>A directive composed of one or more white-space characters shall be executed by reading input until no more valid input can beread, or up to the first byte which is not a white-space character, which remains unread.</p><p>A directive that is an ordinary character shall be executed as follows: the next byte shall be read from the input and comparedwith the byte that comprises the directive; if the comparison shows that they are not equivalent, the directive shall fail, and thediffering and subsequent bytes shall remain unread. Similarly, if end-of-file, an encoding error, or a read error prevents acharacter from being read, the directive shall fail.</p><p>A directive that is a conversion specification defines a set of matching input sequences, as described below for each conversioncharacter. A conversion specification shall be executed in the following steps.</p><p>Input white-space characters (as specified by <a href="isspace.html"><i>isspace</i>()</a> ) shall be skipped, unless theconversion specification includes a <tt>[</tt> , <tt>c</tt> , <tt>C</tt> , or <tt>n</tt> conversion specifier.</p><p>An item shall be read from the input, unless the conversion specification includes an <tt>n</tt> conversion specifier. An inputitem shall be defined as the longest sequence of input bytes (up to any specified maximum field width, which may be measured incharacters or bytes dependent on the conversion specifier) which is an initial subsequence of a matching sequence. The first byte,if any, after the input item shall remain unread. If the length of the input item is 0, the execution of the conversionspecification shall fail; this condition is a matching failure, unless end-of-file, an encoding error, or a read error preventedinput from the stream, in which case it is an input failure.</p><p>Except in the case of a <tt>%</tt> conversion specifier, the input item (or, in the case of a <tt>%n</tt> conversionspecification, the count of input bytes) shall be converted to a type appropriate to the conversion character. If the input item isnot a matching sequence, the execution of the conversion specification fails; this condition is a matching failure. Unlessassignment suppression was indicated by a <tt>'*'</tt> , the result of the conversion shall be placed in the object pointed to bythe first argument following the <i>format</i> argument that has not already received a conversion result if the conversionspecification is introduced by <tt>%</tt> , <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> or in the <i>n</i>th argument if introduced by the charactersequence <tt>"%</tt><i>n</i><tt>$"</tt>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"> If this object does nothave an appropriate type, or if the result of the conversion cannot be represented in the space provided, the behavior isundefined.</p><p>The length modifiers and their meanings are:</p><dl compact><dt><tt>hh</tt></dt><dd>Specifies that a following <tt>d</tt> , <tt>i</tt> , <tt>o</tt> , <tt>u</tt> , <tt>x</tt> , <tt>X</tt> , or <tt>n</tt>conversion specifier applies to an argument with type pointer to <b>signed char</b> or <b>unsigned char</b>.</dd><dt><tt>h</tt></dt><dd>Specifies that a following <tt>d</tt> , <tt>i</tt> , <tt>o</tt> , <tt>u</tt> , <tt>x</tt> , <tt>X</tt> , or <tt>n</tt>conversion specifier applies to an argument with type pointer to <b>short</b> or <b>unsigned short</b>.</dd><dt><tt>l</tt> (ell)</dt><dd>Specifies that a following <tt>d</tt> , <tt>i</tt> , <tt>o</tt> , <tt>u</tt> , <tt>x</tt> , <tt>X</tt> , or <tt>n</tt>conversion specifier applies to an argument with type pointer to <b>long</b> or <b>unsigned long</b>; that a following <tt>a</tt> ,<tt>A</tt> , <tt>e</tt> , <tt>E</tt> , <tt>f</tt> , <tt>F</tt> , <tt>g</tt> , or <tt>G</tt> conversion specifier applies to anargument with type pointer to <b>double</b>; or that a following <tt>c</tt> , <tt>s</tt> , or <tt>[</tt> conversion specifierapplies to an argument with type pointer to <b>wchar_t</b>.</dd><dt><tt>ll</tt> (ell-ell)</dt><dd><br>Specifies that a following <tt>d</tt> , <tt>i</tt> , <tt>o</tt> , <tt>u</tt> , <tt>x</tt> , <tt>X</tt> , or <tt>n</tt> conversionspecifier applies to an argument with type pointer to <b>long long</b> or <b>unsigned long long</b>.</dd><dt><tt>j</tt></dt><dd>Specifies that a following <tt>d</tt> , <tt>i</tt> , <tt>o</tt> , <tt>u</tt> , <tt>x</tt> , <tt>X</tt> , or <tt>n</tt>conversion specifier applies to an argument with type pointer to <b>intmax_t</b> or <b>uintmax_t</b>.</dd><dt><tt>z</tt></dt><dd>Specifies that a following <tt>d</tt> , <tt>i</tt> , <tt>o</tt> , <tt>u</tt> , <tt>x</tt> , <tt>X</tt> , or <tt>n</tt>conversion specifier applies to an argument with type pointer to <b>size_t</b> or the corresponding signed integer type.</dd><dt><tt>t</tt></dt><dd>Specifies that a following <tt>d</tt> , <tt>i</tt> , <tt>o</tt> , <tt>u</tt> , <tt>x</tt> , <tt>X</tt> , or <tt>n</tt>conversion specifier applies to an argument with type pointer to <b>ptrdiff_t</b> or the corresponding <b>unsigned</b> type.</dd><dt><tt>L</tt></dt><dd>Specifies that a following <tt>a</tt> , <tt>A</tt> , <tt>e</tt> , <tt>E</tt> , <tt>f</tt> , <tt>F</tt> , <tt>g</tt> , or<tt>G</tt> conversion specifier applies to an argument with type pointer to <b>long double</b>.</dd></dl><p>If a length modifier appears with any conversion specifier other than as specified above, the behavior is undefined.</p><p>The following conversion specifiers are valid:</p><dl compact><dt><tt>d</tt></dt><dd>Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of <a href="../functions/strtol.html"><i>strtol</i>()</a> with the value 10 for the <i>base</i> argument. In the absence of a size modifier,the application shall ensure that the corresponding argument is a pointer to <b>int</b>.</dd><dt><tt>i</tt></dt><dd>Matches an optionally signed integer, whose format is the same as expected for the subject sequence of <a href="../functions/strtol.html"><i>strtol</i>()</a> with 0 for the <i>base</i> argument. In the absence of a size modifier, theapplication shall ensure that the corresponding argument is a pointer to <b>int</b>.</dd><dt><tt>o</tt></dt><dd>Matches an optionally signed octal integer, whose format is the same as expected for the subject sequence of <a href="../functions/strtoul.html"><i>strtoul</i>()</a> with the value 8 for the <i>base</i> argument. In the absence of a size modifier,the application shall ensure that the corresponding argument is a pointer to <b>unsigned</b>.</dd><dt><tt>u</tt></dt><dd>Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of <a href="../functions/strtoul.html"><i>strtoul</i>()</a> with the value 10 for the <i>base</i> argument. In the absence of a size modifier,the application shall ensure that the corresponding argument is a pointer to <b>unsigned</b>.</dd><dt><tt>x</tt></dt><dd>Matches an optionally signed hexadecimal integer, whose format is the same as expected for the subject sequence of <a href="../functions/strtoul.html"><i>strtoul</i>()</a> with the value 16 for the <i>base</i> argument. In the absence of a size modifier,the application shall ensure that the corresponding argument is a pointer to <b>unsigned</b>.</dd><dt><tt>a</tt>, <tt>e</tt>, <tt>f</tt>, <tt>g</tt></dt><dd><br>Matches an optionally signed floating-point number, infinity, or NaN, whose format is the same as expected for the subject sequenceof <a href="../functions/strtod.html"><i>strtod</i>()</a>. In the absence of a size modifier, the application shall ensure that thecorresponding argument is a pointer to <b>float</b>. <p>If the <a href="../functions/fprintf.html"><i>fprintf</i>()</a> family of functions generates character string representationsfor infinity and NaN (a symbolic entity encoded in floating-point format) to support IEEE Std 754-1985, the<i>fscanf</i>() family of functions shall recognize them as input.</p></dd><dt><tt>s</tt></dt><dd>Matches a sequence of bytes that are not white-space characters. The application shall ensure that the corresponding argumentis a pointer to the initial byte of an array of <b>char</b>, <b>signed char</b>, or <b>unsigned char</b> large enough to accept thesequence and a terminating null character code, which shall be added automatically. <p>If an <tt>l</tt> (ell) qualifier is present, the input is a sequence of characters that begins in the initial shift state. Eachcharacter shall be converted to a wide character as if by a call to the <a href="../functions/mbrtowc.html"><i>mbrtowc</i>()</a>function, with the conversion state described by an <b>mbstate_t</b> object initialized to zero before the first character isconverted. The application shall ensure that the corresponding argument is a pointer to an array of <b>wchar_t</b> large enough toaccept the sequence and the terminating null wide character, which shall be added automatically.</p></dd><dt><tt>[</tt></dt><dd>Matches a non-empty sequence of bytes from a set of expected bytes (the <i>scanset</i>). The normal skip over white-spacecharacters shall be suppressed in this case. The application shall ensure that the corresponding argument is a pointer to theinitial byte of an array of <b>char</b>, <b>signed char</b>, or <b>unsigned char</b> large enough to accept the sequence and aterminating null byte, which shall be added automatically. <p>If an <tt>l</tt> (ell) qualifier is present, the input is a sequence of characters that begins in the initial shift state. Eachcharacter in the sequence shall be converted to a wide character as if by a call to the <a href="../functions/mbrtowc.html"><i>mbrtowc</i>()</a> function, with the conversion state described by an <b>mbstate_t</b> objectinitialized to zero before the first character is converted. The application shall ensure that the corresponding argument is apointer to an array of <b>wchar_t</b> large enough to accept the sequence and the terminating null wide character, which shall beadded automatically.</p><p>The conversion specification includes all subsequent bytes in the <i>format</i> string up to and including the matching rightsquare bracket ( <tt>']'</tt> ). The bytes between the square brackets (the <i>scanlist</i>) comprise the scanset, unless the byteafter the left square bracket is a circumflex ( <tt>'^'</tt> ), in which case the scanset contains all bytes that do not appear inthe scanlist between the circumflex and the right square bracket. If the conversion specification begins with <tt>"[]"</tt> or⌨️ 快捷键说明
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