INDEX(STRING, SUBSTRING, BACK, KIND)

Purpose

Returns the starting position of a substring within a string.

Class

Elemental function

Argument type and attributes

STRING

An INTENT(IN) CHARACTER

SUBSTRING

An INTENT(IN) CHARACTER with the same kind type parameter as STRING.

BACK (optional)

An INTENT(IN) LOGICAL

KIND (optional)

An INTENT(IN) INTEGER scalar. The actual argument corresponding to KIND must be a constant expression.

Result type and attributes

• It is of type integer.
• If KIND is present, the KIND type parameter is that specified by the value of KIND; otherwise, the KIND type parameter is that of default integer type.

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.