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1 @c Copyright (C) 1996, 1997 John W. Eaton |
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2 @c This is part of the Octave manual. |
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3 @c For copying conditions, see the file gpl.texi. |
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4 |
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5 @node Strings |
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6 @chapter Strings |
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7 @cindex strings |
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8 @cindex character strings |
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9 @opindex " |
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10 @opindex ' |
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11 |
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12 A @dfn{string constant} consists of a sequence of characters enclosed in |
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13 either double-quote or single-quote marks. For example, both of the |
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14 following expressions |
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15 |
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16 @example |
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17 @group |
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18 "parrot" |
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19 'parrot' |
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20 @end group |
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21 @end example |
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22 |
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23 @noindent |
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24 represent the string whose contents are @samp{parrot}. Strings in |
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25 Octave can be of any length. |
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26 |
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27 Since the single-quote mark is also used for the transpose operator |
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28 (@pxref{Arithmetic Ops}) but double-quote marks have no other purpose in |
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29 Octave, it is best to use double-quote marks to denote strings. |
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30 |
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31 @c XXX FIXME XXX -- this is probably pretty confusing. |
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32 |
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33 @cindex escape sequence notation |
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34 Some characters cannot be included literally in a string constant. You |
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35 represent them instead with @dfn{escape sequences}, which are character |
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36 sequences beginning with a backslash (@samp{\}). |
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37 |
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38 One use of an escape sequence is to include a double-quote |
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39 (single-quote) character in a string constant that has been defined |
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40 using double-quote (single-quote) marks. Since a plain double-quote |
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41 would end the string, you must use @samp{\"} to represent a single |
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42 double-quote character as a part of the string. The backslash character |
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43 itself is another character that cannot be included normally. You must |
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44 write @samp{\\} to put one backslash in the string. Thus, the string |
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45 whose contents are the two characters @samp{"\} may be written |
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46 @code{"\"\\"} or @code{'"\\'}. Similarly, the string whose contents are |
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47 the two characters @samp{'\} may be written @code{'\'\\'} or @code{"'\\"}. |
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48 |
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49 Another use of backslash is to represent unprintable characters |
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50 such as newline. While there is nothing to stop you from writing most |
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51 of these characters directly in a string constant, they may look ugly. |
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52 |
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53 Here is a table of all the escape sequences used in Octave. They are |
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54 the same as those used in the C programming language. |
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55 |
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56 @table @code |
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57 @item \\ |
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58 Represents a literal backslash, @samp{\}. |
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59 |
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60 @item \" |
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61 Represents a literal double-quote character, @samp{"}. |
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62 |
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63 @item \' |
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64 Represents a literal single-quote character, @samp{'}. |
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65 |
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66 @item \0 |
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67 Represents the ``nul'' character, control-@, ASCII code 0. |
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68 |
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69 @item \a |
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70 Represents the ``alert'' character, control-g, ASCII code 7. |
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71 |
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72 @item \b |
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73 Represents a backspace, control-h, ASCII code 8. |
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74 |
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75 @item \f |
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76 Represents a formfeed, control-l, ASCII code 12. |
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77 |
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78 @item \n |
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79 Represents a newline, control-j, ASCII code 10. |
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80 |
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81 @item \r |
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82 Represents a carriage return, control-m, ASCII code 13. |
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83 |
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84 @item \t |
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85 Represents a horizontal tab, control-i, ASCII code 9. |
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86 |
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87 @item \v |
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88 Represents a vertical tab, control-k, ASCII code 11. |
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89 |
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90 @c We don't do octal or hex this way yet. |
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91 @c |
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92 @c @item \@var{nnn} |
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93 @c Represents the octal value @var{nnn}, where @var{nnn} are one to three |
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94 @c digits between 0 and 7. For example, the code for the ASCII ESC |
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95 @c (escape) character is @samp{\033}.@refill |
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96 @c |
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97 @c @item \x@var{hh}@dots{} |
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98 @c Represents the hexadecimal value @var{hh}, where @var{hh} are hexadecimal |
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99 @c digits (@samp{0} through @samp{9} and either @samp{A} through @samp{F} or |
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100 @c @samp{a} through @samp{f}). Like the same construct in @sc{ansi} C, |
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101 @c the escape |
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102 @c sequence continues until the first non-hexadecimal digit is seen. However, |
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103 @c using more than two hexadecimal digits produces undefined results. (The |
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104 @c @samp{\x} escape sequence is not allowed in @sc{posix} @code{awk}.)@refill |
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105 @end table |
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106 |
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107 Strings may be concatenated using the notation for defining matrices. |
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108 For example, the expression |
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109 |
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110 @example |
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111 [ "foo" , "bar" , "baz" ] |
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112 @end example |
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113 |
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114 @noindent |
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115 produces the string whose contents are @samp{foobarbaz}. @xref{Numeric |
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116 Data Types}, for more information about creating matrices. |
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117 |
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118 @menu |
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119 * Creating Strings:: |
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120 * Searching and Replacing:: |
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121 * String Conversions:: |
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122 * Character Class Functions:: |
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123 @end menu |
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124 |
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125 @node Creating Strings |
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126 @section Creating Strings |
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127 |
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128 @DOCSTRING(blanks) |
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129 |
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130 @DOCSTRING(char) |
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131 |
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132 @DOCSTRING(int2str) |
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133 |
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134 @DOCSTRING(com2str) |
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135 |
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136 @DOCSTRING(strcat) |
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137 |
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138 @DOCSTRING(string_fill_char) |
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139 |
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140 @DOCSTRING(str2mat) |
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141 |
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142 @DOCSTRING(ischar) |
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143 |
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144 @DOCSTRING(isstr) |
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145 |
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146 @node Searching and Replacing |
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147 @section Searching and Replacing |
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148 |
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149 @DOCSTRING(deblank) |
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150 |
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151 @DOCSTRING(findstr) |
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152 |
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153 @DOCSTRING(index) |
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154 |
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155 @DOCSTRING(rindex) |
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156 |
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157 @DOCSTRING(split) |
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158 |
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159 @DOCSTRING(strcmp) |
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160 |
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161 @DOCSTRING(strrep) |
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162 |
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163 @DOCSTRING(substr) |
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164 |
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165 @node String Conversions |
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166 @section String Conversions |
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167 |
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168 @DOCSTRING(bin2dec) |
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169 |
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170 @DOCSTRING(dec2bin) |
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171 |
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172 @DOCSTRING(dec2hex) |
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173 |
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174 @DOCSTRING(hex2dec) |
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175 |
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176 @DOCSTRING(dec2base) |
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177 |
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178 @DOCSTRING(base2dec) |
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179 |
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180 @DOCSTRING(strjust) |
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181 |
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182 @DOCSTRING(str2num) |
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183 |
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184 @DOCSTRING(toascii) |
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185 |
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186 @DOCSTRING(tolower) |
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187 |
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188 @DOCSTRING(toupper) |
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189 |
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190 @DOCSTRING(do_string_escapes) |
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191 |
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192 @DOCSTRING(undo_string_escapes) |
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193 |
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194 @DOCSTRING(warn_num_to_str) |
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195 |
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196 @DOCSTRING(warn_str_to_num) |
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197 |
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198 @DOCSTRING(warn_single_quote_string) |
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199 |
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200 @node Character Class Functions |
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201 @section Character Class Functions |
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202 |
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203 Octave also provides the following character class test functions |
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204 patterned after the functions in the standard C library. They all |
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205 operate on string arrays and return matrices of zeros and ones. |
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206 Elements that are nonzero indicate that the condition was true for the |
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207 corresponding character in the string array. For example, |
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208 |
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209 @example |
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210 @group |
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211 isalpha ("!Q@@WERT^Y&") |
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212 @result{} [ 0, 1, 0, 1, 1, 1, 1, 0, 1, 0 ] |
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213 @end group |
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214 @end example |
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215 |
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216 @DOCSTRING(isalnum) |
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217 |
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218 @DOCSTRING(isalpha) |
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219 |
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220 @DOCSTRING(isascii) |
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221 |
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222 @DOCSTRING(iscntrl) |
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223 |
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224 @DOCSTRING(isdigit) |
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225 |
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226 @DOCSTRING(isgraph) |
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227 |
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228 @DOCSTRING(islower) |
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229 |
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230 @DOCSTRING(isprint) |
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231 |
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232 @DOCSTRING(ispunct) |
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233 |
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234 @DOCSTRING(isspace) |
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235 |
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236 @DOCSTRING(isupper) |
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237 |
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238 @DOCSTRING(isxdigit) |
