Variable arguments using an array code debug help?

[XenoReseller]

I'm not quite sure what I did wrong..It looks fine to me, but I get a segmentation fault.

#include <stdio.h>
#define arrlen(x) (sizeof(x)/sizeof(*(x)))

char stk[3][4] = { "arg","arg2","arg3" };
char stk1[6][4] = { "arg","arg2","arg3","arg4","arg5","arg6" };
    
int varfun(char stack[]){
    int i;
    for(i = 0; i < arrlen(stack); i++){
        printf("%s", stack[i]);
    }
    return 0;
}



int main(){
    varfun(stk);
    printf("----");
    varfun(stk1);
    return 0;
}

[mnd22]

Remember that arrays used as a function parameter are degraded to a pointer. In varfun stack is now *stack not stack[].

Here's a link that explains this further:
Question 6.21

[anduril462]

Actually, stack[] is perfectly valid way to declare a 1-d array function parameter. Question 6.21 is a different issue regarding the sizeof operator. You probably want to read Question 6.4. The issue is most likely with the arrlen() function that is incorrectly reporting the size, since there is no way to know where the end of the list is.

Also, you need to print some newlines ('\n') or call fflush(stdout) periodically. stdout is line buffered, which means nothing shows up until you print a '\n' or call fflush(stdout) explicitly, which makes locating a seg fault via output very difficult since the seg fault may happen much later than the last thing you see printed on the screen.

[FloridaJo]

You may want to pass the size of the array in while it knows the length.

int main(){    
    varfun(*stk,arrlen(stk));
    printf("----");
    varfun(*stk1,arrlen(stk1));
    return 0;
}

int varfun(char stack[],int stsz);

[anduril462]

Wow, I really didn't read that code very carefully. I totally missed the arrlen definition, and it's full of other bugs. You should have had several warnings/errors when you compiled. If not, you need to turn up the warnings on your compiler.

• mnd22 was right as to the reason, though stack[] is still valid. stack is effectively a pointer-to-char, which for which your arrlen wont work (it gives you sizeof(char *) / sizeof(char) regardless of number of elements), hence the seg fault.
• FloridaJo is also right, you need to calculate the length somewhere where the actual stk and stk1 arrays are visible, not the parameter they get passed into, for the reason above.
• Your arrays are not declared properly. "arg2", "arg3", etc require 5 bytes. 4 for the letters and number, and one for the null. Make them stk[3][5] and stk1[6][5].
• Your varfun is declared improperly. You need to pass in an array of char arrays, like so: int varfun(char stack[][5], int size). Then, calculate and pass in the size in main as FloridaJo suggested.