如何将字符串值传递给C中的函数

Question

This bothers me. It gives me a warning of

passing argument 1 of ‘funcName’ discards qualifiers from pointer target type

however, the program to run just fine and printing the submitted value.

The functions are the following

void funcName(char *str) {
    printf("%s", str);
}

void main() {
    funcName("Hello world");
}

output is Hello world.

Answer 1

It's because "Hello, world" is constant, so change the function to

void funcName(const char *text) 
{
    printf("%s\n", text);
}

String literals are constant, they are stored in a read only memory section of your program, passing the pointer without const means that you can accidentally modify it inside the target function, if you do so, that would cause undefined behavior , and the compiler is trying to protect you from that.

Also, void main() is not a standard compliant valid signature for main() , you can find it in old books, previous to the standard, but now it's no longer accepted, accepted and standard signatures are

• int main(void) If you don't handle command line arguments.
• int main(int argc, char **argv) To handle argc parameteres stored in argv that where passed in the command line.

Answer 2

It seems that the problem is that this C program is compiled as a C++ program.

In C++ string literals have types of constant character arrays. So if in a C++ program you supply a string literal as an argument to a function that has the corresponding parameter without the qualifier const then the compiler will issue a message.

If to compile the program as a C program then the code is valid because in C string literals have types of non-constant character arrays and the compiler should not issue a diagnostic message relative to qualifiers.

Nevertheless in any case it is better to declare the function like

void funcName( const char *str );
               ^^^^^^

because in this case the user of the function can be sure that the string passed to the function will not be changed.

Take into account that function main without parameters shall be declared in C like

int main( void )