[c++] Why is conversion from string constant to 'char*' valid in C but invalid in C++

The C++11 Standard (ISO/IEC 14882:2011) says in § C.1.1:

char* p = "abc"; // valid in C, invalid in C++

For the C++ it's OK as a pointer to a String Literal is harmful since any attempt to modify it leads to a crash. But why is it valid in C?

The C++11 says also:

char* p = (char*)"abc"; // OK: cast added

Which means that if a cast is added to the first statement it becomes valid.

Why does the casting makes the second statement valid in C++ and how is it different from the first one? Isn't it still harmful? If it's the case, why did the standard said that it's OK?

You can also use strdup:

char* p = strdup("abc");

It's valid in C for historical reasons. C traditionally specified that the type of a string literal was char * rather than const char *, although it qualified it by saying that you're not actually allowed to modify it.

When you use a cast, you're essentially telling the compiler that you know better than the default type matching rules, and it makes the assignment OK.

You can declare like one of the below options:

char data[] = "Testing String";

or

const char* data = "Testing String";

or

char* data = (char*) "Testing String";