C Programming – Fix Segmentation Fault (Core Dumped) When Changing String Characters

c++

Why changing string characters causes segmentation fault(core dumped):

char *str = "string";
str[0] = 'S'; //segmentation fault(core dumped)

Best Answer

The solution is simple, declare your string in the following way instead

  char str[] = "string";

The reason why you should do this is because of the Undefined behavior. Creating a string with pointers will make your string locate at the read only memory part, so you cannot modify it, whereas another way will also make a copy of your string on the stack. Also check What is the difference between char s[] and char *s in C?

Related Solutions

C – Segmentation Fault When Modifying String Using Pointers

One problem lies with the parameter you pass to the function:

char *string = "foobar";

This is a static string allocated in the read-only portion. When you try to overwrite it with

*end = *begin;

you'll get the segfault.

Try with

char string[] = "foobar";

and you should notice a difference.

The key point is that in the first case the string exists in the read-only segment and just a pointer to it is used while in the second case an array of chars with the proper size is reserved on the stack and the static string (which always exists) is copied into it. After that you're free to modify the content of the array.

Best Answer

Related Solutions

C – Segmentation Fault When Modifying String Using Pointers

Related Question