Language Reference

INDEX(STRING, SUBSTRING, BACK)

Returns the starting position of a substring within a string.

STRING

must be of type character.

SUBSTRING

must be of type character with the same kind type parameter as STRING.

BACK (optional)

must be of type logical.

Class

Elemental function

Result Type and Attributes

Default integer.

Result Value

• Case (i): If BACK is absent or present with the value .FALSE., the result is the minimum positive value of I such that STRING (I : I + LEN (SUBSTRING) - 1) = SUBSTRING or zero if there is no such value. Zero is returned if LEN (STRING) < LEN (SUBSTRING). One is returned if LEN (SUBSTRING) = 0.
• Case (ii): If BACK is present with the value .TRUE., the result is the maximum value of I less than or equal to LEN (STRING) - LEN (SUBSTRING) + 1, such that STRING (I : I + LEN (SUBSTRING) - 1) =  SUBSTRING or zero if there is no such value. Zero is returned if LEN (STRING) < LEN (SUBSTRING) and LEN (STRING) + 1 is returned if LEN (SUBSTRING) = 0.

Examples

INDEX ('FORTRAN', 'R') has the value 3.

INDEX ('FORTRAN', 'R', BACK = .TRUE.) has the value 5.

Notes:

1. When this specific name is passed as an argument, the procedure can only be referenced without the BACK optional argument.