switch brain teaser

switch.c

#include <stdio.h>
#include <stdlib.h>

enum option
{
    OPT_ONE     = 0x01,
    OPT_TWO     = 0x02,
    OPT_THREE   = 0x03,
    OPT_FOUR    = 0x04,
    OPT_MAGIC   = 0x05
};

void test_switch(enum option opt)
{
    switch(opt)
    {
        OPT_ONE:
            fprintf(stdout, "OPT_ONE\n");
            break;
        OPT_TWO:
            fprintf(stdout, "OPT_TWO\n");
            break;
        OPT_THREE:
            fprintf(stdout, "OPT_THREE\n");
            break;
        OPT_FOUR:
            fprintf(stdout, "OPT_FOUR\n");
            break;
        OPT_MAGIC:
            fprintf(stdout, "OPT_MAGIC\n");
            break;
        default:
            fprintf(stdout, "default, no match found.\n");
    };
}

int main(int argc, char* argv[])
{
    test_switch(OPT_MAGIC);
    return EXIT_SUCCESS;
}

OPT_* are labels, not cases, so the program reaches the default case.

Perhaps file this against pygments. Emacs at least highlights the difference.

well... with the right compiler options it doesn't compile.

$ make foo
cc -Werror -Wall -Wextra -Wold-style-definition -Wmissing-declarations -Wredundant-decls -Wmissing-noreturn -Wshadow -Wpointer-arith -Wcast-align -Wwrite-strings -Winline -Wformat-nonliteral -Wformat-security -Wswitch-enum -Wswitch-default -Winit-self -Wmissing-include-dirs -Wundef -Waggregate-return -Wmissing-format-attribute -Wnested-externs -std=c11 -pedantic foo.c -o foo
foo.c: In function ‘test_switch’:
foo.c:16:2: error: enumeration value ‘OPT_ONE’ not handled in switch [-Werror=switch-enum]
switch (opt) {
^
foo.c:16:2: error: enumeration value ‘OPT_TWO’ not handled in switch [-Werror=switch-enum]
foo.c:16:2: error: enumeration value ‘OPT_THREE’ not handled in switch [-Werror=switch-enum]
foo.c:16:2: error: enumeration value ‘OPT_FOUR’ not handled in switch [-Werror=switch-enum]
foo.c:16:2: error: enumeration value ‘OPT_MAGIC’ not handled in switch [-Werror=switch-enum]
foo.c:29:3: error: label ‘OPT_MAGIC’ defined but not used [-Werror=unused-label]
OPT_MAGIC:
^
foo.c:26:3: error: label ‘OPT_FOUR’ defined but not used [-Werror=unused-label]
OPT_FOUR:
^
foo.c:23:3: error: label ‘OPT_THREE’ defined but not used [-Werror=unused-label]
OPT_THREE:
^
foo.c:20:3: error: label ‘OPT_TWO’ defined but not used [-Werror=unused-label]
OPT_TWO:
^
foo.c:17:3: error: label ‘OPT_ONE’ defined but not used [-Werror=unused-label]
OPT_ONE:
^
cc1: all warnings being treated as errors
make: *** [foo] Errore 1
$

@ZeeD that's the reason why this was linked to as a "brain teaser" not a "compiler teaser." Although many brains are also good enough for this one it seems :-)