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Case Sensitivity

GNU Fortran offers the programmer way too much flexibility in deciding how source files are to be treated vis-a-vis uppercase and lowercase characters. There are 66 useful settings that affect case sensitivity, plus 10 settings that are nearly useless, with the remaining 116 settings being either redundant or useless.

None of these settings have any effect on the contents of comments (the text after a c or C in Column 1, for example) or of character or Hollerith constants. Note that things like the E in the statement CALL FOO(3.2E10) and the TO in ASSIGN 10 TO LAB are considered built-in keywords, and so are affected by these settings.

Low-level switches are identified in this section as follows:

Note 1: g77 eventually will support NAMELIST in a manner that is consistent with these source switches--in the sense that input will be expected to meet the same requirements as source code in terms of matching symbol names and keywords (for the exponent letters).

Currently, however, NAMELIST is supported by libg2c, which uppercases NAMELIST input and symbol names for matching. This means not only that NAMELIST output currently shows symbol (and keyword) names in uppercase even if lower-case source conversion (option A2) is selected, but that NAMELIST cannot be adequately supported when source case preservation (option A0) is selected.

If A0 is selected, a warning message will be output for each NAMELIST statement to this effect. The behavior of the program is undefined at run time if two or more symbol names appear in a given NAMELIST such that the names are identical when converted to upper case (e.g. NAMELIST /X/ VAR, Var, var). For complete and total elegance, perhaps there should be a warning when option A2 is selected, since the output of NAMELIST is currently in uppercase but will someday be lowercase (when a libg77 is written), but that seems to be overkill for a product in beta test.

Note 2: Rules for InitialCaps names are:

So A, Ab, ABc, AbC, and Abc are valid InitialCaps names, but AB, A2, and ABC are not. Note that most, but not all, built-in names meet these requirements--the exceptions are some of the two-letter format specifiers, such as BN and BZ.

Here are the names of the corresponding command-line options:

     A0: -fsource-case-preserve
     A1: -fsource-case-upper
     A2: -fsource-case-lower
     B0: -fmatch-case-any
     B1: -fmatch-case-upper
     B2: -fmatch-case-lower
     B3: -fmatch-case-initcap
     C0: -fintrin-case-any
     C1: -fintrin-case-upper
     C2: -fintrin-case-lower
     C3: -fintrin-case-initcap
     D0: -fsymbol-case-any
     D1: -fsymbol-case-upper
     D2: -fsymbol-case-lower
     D3: -fsymbol-case-initcap

Useful combinations of the above settings, along with abbreviated option names that set some of these combinations all at once:

      1: A0--  B0---  C0---  D0---    -fcase-preserve
      2: A0--  B0---  C0---  D-1--
      3: A0--  B0---  C0---  D--2-
      4: A0--  B0---  C0---  D---3
      5: A0--  B0---  C-1--  D0---
      6: A0--  B0---  C-1--  D-1--
      7: A0--  B0---  C-1--  D--2-
      8: A0--  B0---  C-1--  D---3
      9: A0--  B0---  C--2-  D0---
     10: A0--  B0---  C--2-  D-1--
     11: A0--  B0---  C--2-  D--2-
     12: A0--  B0---  C--2-  D---3
     13: A0--  B0---  C---3  D0---
     14: A0--  B0---  C---3  D-1--
     15: A0--  B0---  C---3  D--2-
     16: A0--  B0---  C---3  D---3
     17: A0--  B-1--  C0---  D0---
     18: A0--  B-1--  C0---  D-1--
     19: A0--  B-1--  C0---  D--2-
     20: A0--  B-1--  C0---  D---3
     21: A0--  B-1--  C-1--  D0---
     22: A0--  B-1--  C-1--  D-1--    -fcase-strict-upper
     23: A0--  B-1--  C-1--  D--2-
     24: A0--  B-1--  C-1--  D---3
     25: A0--  B-1--  C--2-  D0---
     26: A0--  B-1--  C--2-  D-1--
     27: A0--  B-1--  C--2-  D--2-
     28: A0--  B-1--  C--2-  D---3
     29: A0--  B-1--  C---3  D0---
     30: A0--  B-1--  C---3  D-1--
     31: A0--  B-1--  C---3  D--2-
     32: A0--  B-1--  C---3  D---3
     33: A0--  B--2-  C0---  D0---
     34: A0--  B--2-  C0---  D-1--
     35: A0--  B--2-  C0---  D--2-
     36: A0--  B--2-  C0---  D---3
     37: A0--  B--2-  C-1--  D0---
     38: A0--  B--2-  C-1--  D-1--
     39: A0--  B--2-  C-1--  D--2-
     40: A0--  B--2-  C-1--  D---3
     41: A0--  B--2-  C--2-  D0---
     42: A0--  B--2-  C--2-  D-1--
     43: A0--  B--2-  C--2-  D--2-    -fcase-strict-lower
     44: A0--  B--2-  C--2-  D---3
     45: A0--  B--2-  C---3  D0---
     46: A0--  B--2-  C---3  D-1--
     47: A0--  B--2-  C---3  D--2-
     48: A0--  B--2-  C---3  D---3
     49: A0--  B---3  C0---  D0---
     50: A0--  B---3  C0---  D-1--
     51: A0--  B---3  C0---  D--2-
     52: A0--  B---3  C0---  D---3
     53: A0--  B---3  C-1--  D0---
     54: A0--  B---3  C-1--  D-1--
     55: A0--  B---3  C-1--  D--2-
     56: A0--  B---3  C-1--  D---3
     57: A0--  B---3  C--2-  D0---
     58: A0--  B---3  C--2-  D-1--
     59: A0--  B---3  C--2-  D--2-
     60: A0--  B---3  C--2-  D---3
     61: A0--  B---3  C---3  D0---
     62: A0--  B---3  C---3  D-1--
     63: A0--  B---3  C---3  D--2-
     64: A0--  B---3  C---3  D---3    -fcase-initcap
     65: A-1-  B01--  C01--  D01--    -fcase-upper
     66: A--2  B0-2-  C0-2-  D0-2-    -fcase-lower

Number 22 is the "strict" ANSI FORTRAN 77 model wherein all input (except comments, character constants, and Hollerith strings) must be entered in uppercase. Use -fcase-strict-upper to specify this combination.

Number 43 is like Number 22 except all input must be lowercase. Use -fcase-strict-lower to specify this combination.

Number 65 is the "classic" ANSI FORTRAN 77 model as implemented on many non-UNIX machines whereby all the source is translated to uppercase. Use -fcase-upper to specify this combination.

Number 66 is the "canonical" UNIX model whereby all the source is translated to lowercase. Use -fcase-lower to specify this combination.

There are a few nearly useless combinations:

     67: A-1-  B01--  C01--  D--2-
     68: A-1-  B01--  C01--  D---3
     69: A-1-  B01--  C--23  D01--
     70: A-1-  B01--  C--23  D--2-
     71: A-1-  B01--  C--23  D---3
     72: A--2  B01--  C0-2-  D-1--
     73: A--2  B01--  C0-2-  D---3
     74: A--2  B01--  C-1-3  D0-2-
     75: A--2  B01--  C-1-3  D-1--
     76: A--2  B01--  C-1-3  D---3

The above allow some programs to be compiled but with restrictions that make most useful programs impossible: Numbers 67 and 72 warn about any user-defined symbol names (such as SUBROUTINE FOO); Numbers 68 and 73 warn about any user-defined symbol names longer than one character that don't have at least one non-alphabetic character after the first; Numbers 69 and 74 disallow any references to intrinsics; and Numbers 70, 71, 75, and 76 are combinations of the restrictions in 67+69, 68+69, 72+74, and 73+74, respectively.

All redundant combinations are shown in the above tables anyplace where more than one setting is shown for a low-level switch. For example, B0-2- means either setting 0 or 2 is valid for switch B. The "proper" setting in such a case is the one that copies the setting of switch A--any other setting might slightly reduce the speed of the compiler, though possibly to an unmeasurable extent.

All remaining combinations are useless in that they prevent successful compilation of non-null source files (source files with something other than comments).