11.1.3 Case Sensitivity

C and Fortran take opposite perspectives on case sensitivity:

• C is case sensitive—case matters.

• Fortran ignores case by default.

The f95 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 Fortran program with the -U option, which tells the compiler 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 f95 -U compiler option.