Text manipulation with GAMAP: Difference between revisions
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== Strings and bytes == | == Strings and bytes == | ||
In IDL, a string is equivalent to an array of byte values. A byte is a collection of 8 bits and may express values from 0-255. The [http://www.asciitable.com/ ASCII collating sequence] has 255 values. (Actually, the original ASCII table had 128 values, but this was later extended to 255 values to include special characters.) One byte represents a single text character. | In IDL, a string of text characters is equivalent to an array of byte values. A byte is a collection of 8 bits and may express values from 0-255. The [http://www.asciitable.com/ ASCII collating sequence] has 255 values. (Actually, the original ASCII table had 128 values, but this was later extended to 255 values to include special characters.) One byte represents a single text character. | ||
This means that it is easy to convert between strings and bytes. If you have an array of bytes, you can use any of the IDL string routines on them, for example: | This means that it is easy to convert between strings and bytes. If you have an array of bytes, you can use any of the IDL string routines on them, for example: | ||
Revision as of 19:36, 15 April 2008
Strings and bytes
In IDL, a string of text characters is equivalent to an array of byte values. A byte is a collection of 8 bits and may express values from 0-255. The ASCII collating sequence has 255 values. (Actually, the original ASCII table had 128 values, but this was later extended to 255 values to include special characters.) One byte represents a single text character.
This means that it is easy to convert between strings and bytes. If you have an array of bytes, you can use any of the IDL string routines on them, for example:
IDL> byte_array = [ 72B, 69B, 76B, 76B, 79B ] IDL> help, byte_array BYTE_ARRAY BYTE = Array[5] IDL> print, strtrim( byte_array, 2 ) HELLO
GAMAP comes with a very useful routine called str2byte.pro. This allows you to take a text string and to convert it into the equivalent array of bytes.
IDL> str = 'IDL is neat!' IDL> byte_array = str2byte( str, strlen( str ) ) IDL> help, byte_array BYTE_ARRAY BYTE = Array[12] IDL> print, byte_array 73 68 76 32 105 115 32 110 101 97 116 33
Note that we used IDL's STRLEN function to return the length of the string.
For more information about IDL's string functions, please see http://idlastro.gsfc.nasa.gov/idl_html_help/Strings.html.