ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings] error shown in Visual Studio code while trying to run C code

Question

I am trying to run the following code which takes string parameter and returns the length of the string in characters in C language using Visual Studio Code, but I am getting:

Error message:

ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]

Here is my code:

int str_length(char *mystring){

    int i=0;

    for(i=0; mystring[i]!='\0'; i++);

    return i;
}

void alpha(){

    printf("%d\n", str_length("-h=123"));

    printf("%d\n", str_length(""));

}

I am stuck with this task, maybe you could provide a possible solution or some parts of the code that I have to change?

Answer 1

It means that you are compiling your program as a C++ program.

In C++ opposite to C string literals have types of constant character arrays.

From the C++ 17 Standard (5.13.5 String literals)

8 Ordinary string literals and UTF-8 string literals are also referred to as narrow string literals. A narrow string literal has type “array of n const char” , where n is the size of the string as defined below, and has static storage duration (6.7).

But even in C the function parameter shall have the qualifier const because the function does not change the passed string. The function can look the following way

size_t str_length( const char *mystring )
{
    size_t i = 0;

    while ( mystring[i] != '\0' ) i++;

    return i;
}

So within the function alpha you need to write

printf("%zu\n", str_length("-h=123"));

printf("%zu\n", str_length(""));

changing the conversion specifier from %d to %zu . The signed type int can be not large enough to store the length of an arbitrary string.