Question

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Why do I get a segmentation fault when writing to a string?

I want to write a function that reverses the given string passed into it. But, I can not. If I supply the doReverse function (see code below) with a character array, my code works well.

I can’t figure out why this does not work. I am able to access str[0] in doReverse, but I can’t change any value of the array by using a char pointer. Any ideas?

void doReverse(char *str) {     str[0] = 'b'; }  void main(void) {     char *str = 'abc';     doReverse(str);     puts(str); } 

Update:

I know how to do write a reverse function by passing a character array to it:

void reverse1(char p[]) {     int i, temp, y;      for (i = 0, y = strlen(p); i < y; ++i, --y) {         temp = p[y-1];         p[y-1] = p[i];         p[i] = temp;     } } 

But, I want to write another version that gets a char pointer as a parameter.

Answer 1

The simplest solution is to change the declaration of str to

char str[] = 'abc'; 

This makes str an array of char that is initialized to the string ‘abc’. Currently you have str as a pointer-to-char initialized to point to a string described by a string literal. There is a key difference: string literals are read-only to give the compiler maximum flexibility on where to store them; it is UB to modify them. But arrays of char are mutable, and so it’s okay to modify those.

PS. main() returns an int.