bus error when trying to access character on a string in C
Question
I have used this line of code many times (update: when string was a parameter to the function!), however when I try to do it now I get a bus error (both with gcc and clang). I am reproducing the simplest possible code;
char *string = "this is a string";
char *p = string;
p++;
*p='x'; //this line will cause the Bus error
printf("string is %s\n",string);
Why am I unable to change the second character of the string using the p pointer?
Solution
You are trying to modify read only memory (where that string literal is stored). You can use a char array instead if you need to modify that memory.
char str[] = "This is a string";
str[0] = 'S'; /* works */
I have used this line of code many times..
I sure hope not. At best you would get a segfault (I say "at best" because attempting to modify readonly memory is unspecified behavior, in which case anything can happen, and a crash is the best thing that can happen).
When you declare a pointer to a string literal it points to read only memory in the data segment (look at the assembly output if you like). Declaring your type as a char[] will copy that literal onto the function's stack, which will in turn allow it to be modified if needed.