C++ deprecated conversion from string constant to 'char*'

Solution 1:

This is an error message you see whenever you have a situation like the following:

char* pointer_to_nonconst = "string literal";

Why? Well, C and C++ differ in the type of the string literal. In C the type is array of char and in C++ it is constant array of char. In any case, you are not allowed to change the characters of the string literal, so the const in C++ is not really a restriction but more of a type safety thing. A conversion from const char* to char* is generally not possible without an explicit cast for safety reasons. But for backwards compatibility with C the language C++ still allows assigning a string literal to a char* and gives you a warning about this conversion being deprecated.

So, somewhere you are missing one or more consts in your program for const correctness. But the code you showed to us is not the problem as it does not do this kind of deprecated conversion. The warning must have come from some other place.

Solution 2:

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.

Solution 3:

As answer no. 2 by fnieto - Fernando Nieto clearly and correctly describes that this warning is given because somewhere in your code you are doing (not in the code you posted) something like:

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

However, if you want to keep your code warning-free as well then just make respective change in your code:

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

That is, simply cast the string constant to (char *).

Solution 4:

There are 3 solutions:

Solution 1:

const char *x = "foo bar";

Solution 2:

char *x = (char *)"foo bar";

Solution 3:

char* x = (char*) malloc(strlen("foo bar")+1); // +1 for the terminator
strcpy(x,"foo bar");

Arrays also can be used instead of pointers because an array is already a constant pointer.

Solution 5:

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.