pointer error

[questionit]

Hi experts

Why i get run-time error with this:

char *temp ="string";

temp[2] = '\0'; // < get errror here?

Memory address is not being touched but only a value which resides on the momory is being altered, there should not be any problem doing this?

Please explain
Thanks

[Banfa]

temp is pointing to a string constant. String constants on some platforms are just that, constant. Trying to alter them causes a memory access exception.

In general it is best to avoid altering a string constant, if you need to modify it copy it to a variable or allocated data and alter the copy.

[nmadct]

Hi experts

Why i get run-time error with this:

char *temp ="string";

temp[2] = '\0'; // < get errror here?

Memory address is not being touched but only a value which resides on the memory is being altered, there should not be any problem doing this?

A string literal like "string" is stored in non-writable memory (with most C compilers). So, the pointer temp is pointing to a memory location that you're not allowed to write to. When you try to write to it anyway, it causes a runtime error. There are a couple of ways you can get around this problem:

char temp[] = "string"; // works if temp is a global variable

char temp[7]; // remember to allocate an extra byte for the terminating null!
strcpy(temp, "string");

Either one of these approaches gives you a buffer in writable memory that is filled with the value "string".