Case Sensitivity

C and Fortran take opposite perspectives on case sensitivity:

• C is case sensitive--case matters.

• Fortran ignores case.

The f77 and f90 default is to ignore case by converting subprogram names to lowercase. It converts all uppercase letters to lowercase letters, except within character-string constants.

There are two usual solutions to the uppercase/lowercase problem:

• In the C subprogram, make the name of the C function all lowercase.

• Compile the f77 program with the -U option, which tells f77 to preserve existing uppercase/lowercase distinctions on function/subprogram names.

Use one of these two solutions, but not both.

Most examples in this chapter use all lowercase letters for the name in the C function, and do not use the f77 -U compiler option. (f90 does not have an equivalent option.)