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466
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1 <refentry id="scanf">
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2 <refnamediv>
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574
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3 <refname>Scanf</refname>
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4 <refname>Fscanf</refname>
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5 <refname>Sscanf</refname>
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6 <refpurpose>input string interpretation</refpurpose>
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466
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7 </refnamediv>
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8
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9 <refsynopsisdiv>
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10 <funcsynopsis>
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468
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11 <funcsynopsisinfo>
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12 #include <stdio.h>
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13 </funcsynopsisinfo>
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466
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14 <funcprototype>
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574
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15 <funcdef><function>fscanf</function></funcdef>
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16 <paramdef>FILE *<parameter>fp</parameter></paramdef>
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17 <paramdef>char *<parameter>control</parameter></paramdef>
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18 <paramdef>char *<parameter>pointer...</parameter></paramdef>
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19 </funcprototype>
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20
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21 <funcprototype>
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466
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22 <funcdef><function>scanf</function></funcdef>
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574
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23 <paramdef>char *<parameter>control</parameter></paramdef>
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24 <paramdef>char *<parameter>pointer...</parameter></paramdef>
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466
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25 </funcprototype>
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574
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26
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27 <funcprototype>
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28 <funcdef><function>sscanf</function></funcdef>
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29 <paramdef>char *<parameter>string</parameter></paramdef>
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30 <paramdef>char *<parameter>control</parameter></paramdef>
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31 <paramdef>char *<parameter>pointer...</parameter></paramdef>
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32 </funcprototype>
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33
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466
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34 </funcsynopsis>
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35
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36 </refsynopsisdiv>
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37
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38 <refsect1><title>Description</title>
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39 <para>
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640
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40 These functions perform the complement to "printf()" etc.
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466
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41 </para>
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605
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42 <para>
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43 Fscanf performs conversions from the file "fp", scanf from the
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44 standard input, and sscanf from the string pointed to by
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45 "string".
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46 </para>
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47 <para>
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48 Each function expects a control string containing conversion
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49 specifications, and zero or more pointers to objects into which
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50 the converted values are stored.
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51 </para>
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52 <para>
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53 The control string may contain three types of fields:
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54 <orderedlist numeration="loweralpha" spacing="compact">
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55 <listitem><para>
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56 Space, tab characters, or "\n" which match any of
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57 the three in the input.
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58 </para></listitem>
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59 <listitem><para>
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60 Characters not among the above and not "%" which must
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61 match characters in the input.
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62 </para></listitem>
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63 <listitem><para>
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64 A "%" followed by an optional "*" indicates
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65 suppression of assignment, an optional field width
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66 maximum and a conversion character indicating the
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67 type expected.
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68 </para></listitem>
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69 </orderedlist>
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70 </para>
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71 <para>
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72 A conversion character controls the conversion to be applied
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73 to the next field and indicates the type of the corresponding
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74 pointer argument. A field consists of consecutive non-space
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75 characters and ends at either a character inappropiate for the
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76 conversion or when a specified field is exhausted.
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77 When one field is finished, white-space characters are passed
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78 over until the next field is found.
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79 </para>
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80 <informaltable frame="none">
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81 <tgroup cols="2">
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640
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82 <colspec colwidth="0.5in"/>
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83 <colspec colwidth="3.5in"/>
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605
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84 <tbody>
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85 <row>
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86 <entry>d</entry>
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87 <entry>A decimal string is to be converted to an integer.</entry>
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88 </row>
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89 <row>
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90 <entry>o</entry>
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91 <entry>An octal string; the coresponding argument should
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92 point to an integer.</entry>
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93 </row>
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94 <row>
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95 <entry>x</entry>
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96 <entry>A hexadecimal string for conversion to an integer.</entry>
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97 </row>
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98 <row>
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99 <entry>s</entry>
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100 <entry>A string of non-space characters is expected and
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101 will be copied to the buffer pointed to by the
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102 corresponding argument and a null ("\0") appended.
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103 The user must ensure that the buffer is large
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104 enough. The input string is considered terminated
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105 by a space, tab of ("\n").</entry>
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106 </row>
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107 <row>
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108 <entry>c</entry>
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109 <entry>A character is expected and is copied into the byte
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110 pointed to by the argument. The white-space
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111 skipping is suppressed for this conversion. If a
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112 field width is given, the argument is assumed to
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113 point to a character array and the number of
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114 characters indicated is copied to it. NOTE to ensure
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115 that the next non-white-space character is read use
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116 "%1s" and that TWO bytes are pointed to by the
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117 argument.</entry>
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118 </row>
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119 <row>
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120 <entry>e,f</entry>
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121 <entry>A floating point representation is expected on the
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122 input and the argument must be a pointer to a float.
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123 Any of the usual ways of writing floating point
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124 numbers are recognized.</entry>
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125 </row>
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126 <row>
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127 <entry>[</entry>
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128 <entry>This denotes the start of a set of match characters;
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129 the inclusion or exclusion of which delimits the
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130 input field. The white-space skipping is
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131 suppressed. The corresponding argument should be a
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132 pointer to a character array. If the first
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133 character in the match string is not "^",
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134 characters are copied from the input as long as they
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135 can be found in the match string. If the first
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136 character is the "^", copying continues while characters
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137 cannot be found in the match string. The match
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138 string is delimited by a "]".</entry>
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139 </row>
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140 <row>
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141 <entry>D,O,X</entry>
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142 <entry>Similar to d,o,x above, but the corresponding
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143 argument is considered to point to a long integer.</entry>
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144 </row>
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145 <row>
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146 <entry>E,F</entry>
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147 <entry>Similar to e,f above, but the corresponding
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148 should point to a double.</entry>
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149 </row>
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150 <row>
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151 <entry>%</entry>
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152 <entry>A match for "%" is sought; no conversion takes place.</entry>
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153 </row>
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154 </tbody>
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155 </tgroup>
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156 </informaltable>
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157 <para>
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158 Each of the functions returns a count of the number of
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159 fields successfully matched and assigned.
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160 </para>
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161 </refsect1>
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162
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163 <refsect1><title>Caveats</title>
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164 <para>
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165 The returned count of matches/assigments does not include
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166 character matches and assigments suppressed by "*". The
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167 arguments must ALL be pointers. It is a common error to call
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168 scanf with the value of an item rather than a pointer to it.
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169 </para>
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466
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170 </refsect1>
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542
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171
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552
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172 <refsect1><title>Diagnostics</title>
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173 <para>
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174 These functions return EOF on end of input or error and a count
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175 which is shorter than expected for unexpected or unmatched
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176 items.
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177 </para>
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178 </refsect1>
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179
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542
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180 <refsect1><title>See Also</title>
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181 <para>
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605
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182 <link linkend="atof">Atoi(), atof()</link>,
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542
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183 <link linkend="getc">getc()</link>,
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184 <link linkend="printf">printf()</link>
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185 Kernighan and Ritchie pp 147-150
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186 </para>
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187 </refsect1>
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188
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466
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189 </refentry>
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