Symbolic Names

The items in the following table can have symbolic names:

Table 1-2 Items with Symbolic Names

Symbolic constants  Variables  Arrays  Structures @  Records @  Record fields @

Labeled commons  Namelist groups @  Main programs   Block data  Subroutines   Functions   Entry points

The following restrictions apply:

• Symbolic names can any number of characters long. The standard is 6. @

• Symbolic names consist of letters, digits, the dollar sign ($), and the underscore character (_). $ and _ are not standard. @

• Symbolic names generally start with a letter--never with a digit or dollar sign ($). Names that start with an underscore (_) are allowed, but may conflict with names in the Fortran and system libraries.

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  Note -

  Procedure names that begin with exactly two underscores are considered special support functions internal to the compiler. Avoid naming functions or subroutines with exactly two initial underscores (for example _ _xfunc) as this will conflict with the compiler's usage. @

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• Uppercase and lowercase are not significant; the compiler converts them all to lowercase. The -U option on the f77 command line overrides this default, thereby preserving any uppercase used in your source file. @

  Example: These names are equivalent with the default in effect:

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         ATAD = 1.0E-6 
         Atad = 1.0e-6 

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• The space character is not significant.

  Example: These names are equivalent:

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         IF ( X .LT. ATAD ) GO TO 9 
         IF ( X .LT. A TAD ) GO TO 9 
         IF(X.LT.ATAD)GOTO9 

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  Here are some sample symbolic names:

Table 1-3 Sample Symbolic Names

Valid	Invalid	Reason
X2	2X	Starts with a digit.
DELTA_TEMP	_DELTA_TEMP	Starts with an _ (reserved for the compiler).
Y$Dot	Y|Dot	There is an invalid character |.

• In general, for any single program unit, different entities cannot have the same symbolic name. The exceptions are:

  • A variable or array can have the same name as a common block.

  • A field of a record can have the same name as a structure. @

  • A field of a record can have the same name as a field at a different level of the structure. @

• Throughout any program of more than one programming unit, no two of the following can have the same name:

  • Block data subprograms

  • Common blocks

  • Entry points

  • Function subprograms

  • Main program

  • Subroutines