C++ deprecated conversion from string constant to

Question

I have a class with a private char str[256];

and for it I have an explicit constructor:

explicit myClass(const char *func)
{
    strcpy(str,func);
}

I call it as:

myClass obj("example");

When I compile this I get the following warning:

deprecated conversion from string constant to 'char*'

Why is this happening?

Answer 1

In fact a string constant literal is neither a const char * nor a char* but a char[]. Its quite strange but written down in the c++ specifications; If you modify it the behavior is undefined because the compiler may store it in the code segment.

Answer 2

I solve this problem by adding this macro in the beginning of the code, somewhere. Or add it in <iostream>, hehe.

 #define C_TEXT( text ) ((char*)std::string( text ).c_str())

Answer 3

I also got the same problem. And what I simple did is just adding const char* instead of char*. And the problem solved. As others have mentioned above it is a compatible error. C treats strings as char arrays while C++ treat them as const char arrays.

Answer 4

The warning:

deprecated conversion from string constant to 'char*'

is given because you are doing somewhere (not in the code you posted) something like:

void foo(char* str);
foo("hello");

The problem is that you are trying to convert a string literal (with type const char[]) to char*.

You can convert a const char[] to const char* because the array decays to the pointer, but what you are doing is making a mutable a constant.

This conversion is probably allowed for C compatibility and just gives you the warning mentioned.

Answer 5

The following illustrates the solution, assign your string to a variable pointer to a constant array of char (a string is a constant pointer to a constant array of char - plus length info):

#include <iostream>

void Swap(const char * & left, const char * & right) {
    const char *const temp = left;
    left = right;
    right = temp;
}

int main() {
    const char * x = "Hello"; // These works because you are making a variable
    const char * y = "World"; // pointer to a constant string
    std::cout << "x = " << x << ", y = " << y << '\n';
    Swap(x, y);
    std::cout << "x = " << x << ", y = " << y << '\n';
}

Answer 6

Maybe you can try this:

void foo(const char* str) 
{
    // Do something
}

foo("Hello")

It works for me