Segmentation Fault when using strupr(...) with GCC compiler

When run following code after compiling on gcc,I get segmentation fault.

#i开发者_运维知识库nclude <stdio.h>
#include <string.h>

int main(void)
{
    struct emp
    {
        char *n;
        int age;
    };

    struct emp e1={"David",23};
    struct emp e2=e1;
    strupr(e2.n);
    printf("%s\n%s\n",e1.n,e2.n);
    return(0);
}

String literals like "David" cannot be altered, which is what you're doing when you call strupr. You should copy the string (e.g. with strdup) before.

You are getting a seg fault because

struct emp e1={"David",23};

"David" resides in data, so it is a read-only, or const, string.

When you

strupr(e2.n);

You are trying to modify that same const string.

Working code:

struct emp e2;
e2.age = e1.age;
e2.n = (char *)malloc(SOME_SIZE);
strcpy(e2.n, e1.n); //here you copy the contents of the read-only string to newly allocated memory
strupr(e2.n);
printf(...);
free(e2.n);
return 0;

By doing struct emp e1={"David",23}; you have made "David" a string literal, which is read-only in nature. In the executable it is stored in the .rodata or equivalent section of the executable, which is read-only. by the strupr () you are attempting to modify this read-only data, and thus a segmentation fault.