LinuxQuestions.org - casting a const char into a char

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casting a const char into a char

What happens when you cast a const char* to a char*?

Code:

const char* str1 = "test";

char *str2 = (char*) str1;

Is str2 now a new string? Does it need to be freed?

Hi

Short answer: no :)

But I'll try to explain. Strings in C are confusing. It's usually better to think of them as an array of characters.

These lines are equivalent:

Code:

const char *str = "test";

const char str[5] = { 't','e','s','t','\0' };

Code:

char *str2 = (char*) str1;

This makes a new pointer variable called str2 and it points to str1 (the 't' character). If you try to modify that string, you will get a segmentation fault.

To make a new string that's a pointer to heap memory that you can modify and then free, use the strdup function.

Code:

char *str2 = strdup(str1);

The strdup allocates memory for the string with malloc, and then copies the string to that memory, and finally it returns a pointer to the new allocated memory.

Right. I saw this in some code, and I can't figure out why the author wanted to cast out the const'ness of the string

Quote:

Originally Posted by MicahCarrick

Right. I saw this in some code, and I can't figure out why the author wanted to cast out the const'ness of the string

well it would make sense if the string in question is not a literal.