HP OpenVMS Systems Documentation
HP OpenVMS DCL Dictionary
Locates a specified portion of a character string and returns as an integer the offset of the first character. (An offset is the position of a character or a substring relative to the begining of the string. The first character in a string is always offset position 0 from the beginning of the string.)
An integer value representing the offset of the substring argument. An offset is the position of a character or a substring relative to the beginning of the string. The first character in a string is always offset position 0 from the beginning of the string (which always begins at the leftmost character).
If the substring is not found, the F$LOCATE function returns an offset of the last character in the character string plus 1. (This equals the length of the string.)
$ FILE_SPEC = "MYFILE.DAT;1" $ NAME_LENGTH = F$LOCATE(".",FILE_SPEC)
The F$LOCATE function in this example returns the position of the period (.) in the string with respect to the beginning of the string. The period is in offset position 6, so the value 6 is assigned to the symbol NAME_LENGTH. Note that NAME_LENGTH also equals the length of the file name portion of the file specification MYFILE.DAT, that is, 6.
The substring argument, the period, is specified as a string literal and is therefore enclosed in quotation marks (" "). The string argument FILE_SPEC is a symbol, so it should not be placed within quotation marks. It is automatically replaced by its current value during the processing of the function.
$ INQUIRE TIME "Enter time" $ IF F$LOCATE(":",TIME) .EQ. F$LENGTH(TIME) THEN - GOTO NO_COLON
This section of a command procedure compares the results of the F$LOCATE and F$LENGTH functions to see if they are equal. This technique is commonly used to determine whether a character or substring is contained in a string.
In the example, the INQUIRE command prompts for a time value and assigns the user-supplied time to the symbol TIME. The IF command checks for the presence of a colon (:) in the string entered in response to the prompt. If the value returned by the F$LOCATE function equals the value returned by the F$LENGTH function, the colon is not present. You use the .EQ. operator (rather than .EQS.) because the F$LOCATE and F$LENGTH functions return integer values.
Note that quotation marks are used around the substring argument, the colon, because it is a string literal; however, the symbol TIME does not require quotation marks because it is automatically evaluated as a string expression.