C++, char* string modification

Question

I am new to C++. I have a program:

#include <iostream>

int main()
{
   char* str = "Test";
   *str = 'S';
}

The question is, why *str = 'S' crashes the program? As far as I know str must be pointing to the first character of the string (well, char array), so in theory I should be able to modify it. Is it because the memory is read-only for defined constant values? I am using gcc 5.3.0.

"Is it because the memory is read-only for defined constant values?" Nailed it. — user4581301, Apr 01 '17 at 15:40
I think you can replace char* to char[] and then you can modify it. — Peter Lenkefi, Apr 01 '17 at 15:41

score 3 · Accepted Answer · answered Apr 01 '17 at 15:33

why *str = 'S' crashes the program?

Because you're not allowed to modify string literals. The C++ standard allows them to be stored in read-only memory.

In fact, if you enable compiler warnings, you get:

prog.cc:5:16: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
    char* str = "Test";
                ^~~~~~

Always use const char* when pointing to string literals:

C++, char* string modification

1 Answers1