Clang: strict-prototypes warning ignored, so bad code proliferates

Number:rdar://23116994 Date Originated:14-Oct-2015 03:33 PM
Status:Open Resolved:
Product:Developer Tools Product Version:Xcode 7.0.1 (7A1001)
Classification:UI/Usability Reproducible:Always
The -Wstrict-prototypes warning from GCC is not implemented in Clang. In C and Objective-C code, many developers mistakenly use ‘()’ for a function or block parameters expecting it to mean “no arguments” where it actually means “unspecified arguments”. This has been an “obsolescent feature” since C89 and ANSI-C.

This leads to type mis-matches, where a block typed ‘void (^)()’ can be passed as a parameter to ‘void (^)(id obj, float f)’ without warning resulting in issues at runtime (unexpected values, EXC_BAD_ACCESS, etc.). There should be a diagnostic when first creating a variable of a function or block type with unspecified arguments.

Steps to reproduce:
Compile (with -Weverything) and run:

int main(int argc, const char *argv[]) {
    void (^block)() = ^(NSInteger arg) {
        printf(“arg = %ld\n”, arg);
    return 0;

Expected Results:
Warning at line 2 (example using GCC’s language; actual wording should be more effective):
  warning: block declaration isn’t a prototype [-Wstrict-prototypes]

Actual Results:
No warnings are generated; logged output is:
arg = 42
arg = 4294967295

Xcode Version/Build & OS X Version/Build:
Xcode 7.0.1 (7A1001)
OS X 10.10.5 (14F27)

Additional Notes:
See also


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