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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, Data Structures, Numeric Data Types, Top |
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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 \a |
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67 Represents the ``alert'' character, control-g, ASCII code 7. |
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68 |
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69 @item \b |
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70 Represents a backspace, control-h, ASCII code 8. |
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71 |
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72 @item \f |
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73 Represents a formfeed, control-l, ASCII code 12. |
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74 |
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75 @item \n |
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76 Represents a newline, control-j, ASCII code 10. |
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77 |
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78 @item \r |
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79 Represents a carriage return, control-m, ASCII code 13. |
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80 |
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81 @item \t |
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82 Represents a horizontal tab, control-i, ASCII code 9. |
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83 |
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84 @item \v |
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85 Represents a vertical tab, control-k, ASCII code 11. |
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86 |
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87 @c We don't do octal or hex this way yet. |
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88 @c |
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89 @c @item \@var{nnn} |
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90 @c Represents the octal value @var{nnn}, where @var{nnn} are one to three |
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91 @c digits between 0 and 7. For example, the code for the ASCII ESC |
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92 @c (escape) character is @samp{\033}.@refill |
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93 @c |
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94 @c @item \x@var{hh}@dots{} |
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95 @c Represents the hexadecimal value @var{hh}, where @var{hh} are hexadecimal |
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96 @c digits (@samp{0} through @samp{9} and either @samp{A} through @samp{F} or |
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97 @c @samp{a} through @samp{f}). Like the same construct in @sc{ansi} C, |
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98 @c the escape |
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99 @c sequence continues until the first non-hexadecimal digit is seen. However, |
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100 @c using more than two hexadecimal digits produces undefined results. (The |
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101 @c @samp{\x} escape sequence is not allowed in @sc{posix} @code{awk}.)@refill |
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102 @end table |
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103 |
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104 Strings may be concatenated using the notation for defining matrices. |
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105 For example, the expression |
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106 |
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107 @example |
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108 [ "foo" , "bar" , "baz" ] |
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109 @end example |
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110 |
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111 @noindent |
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112 produces the string whose contents are @samp{foobarbaz}. @xref{Numeric |
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113 Data Types}, for more information about creating matrices. |
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114 |
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115 @menu |
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116 * Creating Strings:: |
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117 * Searching and Replacing:: |
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118 * String Conversions:: |
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119 * Character Class Functions:: |
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120 @end menu |
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121 |
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122 @node Creating Strings, Searching and Replacing, Strings, Strings |
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123 @section Creating Strings |
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124 |
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125 @DOCSTRING(blanks) |
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126 |
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127 @DOCSTRING(int2str) |
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128 |
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129 @DOCSTRING(setstr) |
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130 |
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131 @DOCSTRING(strcat) |
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132 |
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133 @DOCSTRING(string_fill_char) |
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134 |
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135 @DOCSTRING(str2mat) |
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136 |
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137 @DOCSTRING(isstr) |
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138 |
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139 @node Searching and Replacing, String Conversions, Creating Strings, Strings |
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140 @section Searching and Replacing |
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141 |
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142 @DOCSTRING(deblank) |
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143 |
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144 @DOCSTRING(findstr) |
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145 |
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146 @DOCSTRING(index) |
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147 |
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148 @DOCSTRING(rindex) |
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149 |
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150 @DOCSTRING(split) |
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151 |
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152 @DOCSTRING(strcmp) |
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153 |
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154 @DOCSTRING(strrep) |
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155 |
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156 @DOCSTRING(substr) |
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157 |
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158 @node String Conversions, Character Class Functions, Searching and Replacing, Strings |
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159 @section String Conversions |
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160 |
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161 @DOCSTRING(bin2dec) |
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162 |
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163 @DOCSTRING(dec2bin) |
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164 |
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165 @DOCSTRING(dec2hex) |
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166 |
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167 @DOCSTRING(hex2dec) |
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168 |
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169 @DOCSTRING(str2num) |
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170 |
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171 @DOCSTRING(toascii) |
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172 |
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173 @DOCSTRING(tolower) |
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174 |
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175 @DOCSTRING(toupper) |
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176 |
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177 @DOCSTRING(undo_string_escapes) |
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178 |
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179 @DOCSTRING(implicit_num_to_str_ok) |
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180 |
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181 @DOCSTRING(implicit_str_to_num_ok) |
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182 |
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183 @node Character Class Functions, , String Conversions, Strings |
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184 @section Character Class Functions |
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185 |
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186 Octave also provides the following character class test functions |
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187 patterned after the functions in the standard C library. They all |
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188 operate on string arrays and return matrices of zeros and ones. |
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189 Elements that are nonzero indicate that the condition was true for the |
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190 corresponding character in the string array. For example, |
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191 |
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192 @example |
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193 @group |
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194 isalpha ("!Q@@WERT^Y&") |
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195 @result{} [ 0, 1, 0, 1, 1, 1, 1, 0, 1, 0 ] |
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196 @end group |
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197 @end example |
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198 |
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199 @DOCSTRING(isalnum) |
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200 |
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201 @DOCSTRING(isalpha) |
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202 |
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203 @DOCSTRING(isascii) |
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204 |
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205 @DOCSTRING(iscntrl) |
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206 |
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207 @DOCSTRING(isdigit) |
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208 |
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209 @DOCSTRING(isgraph) |
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210 |
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211 @DOCSTRING(islower) |
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212 |
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213 @DOCSTRING(isprint) |
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214 |
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215 @DOCSTRING(ispunct) |
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216 |
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217 @DOCSTRING(isspace) |
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218 |
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219 @DOCSTRING(isupper) |
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220 |
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221 @DOCSTRING(isxdigit) |
