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carrayspointersunary-operator

What is the use of unary plus operator in pointer initialization?

I know that C & C++ both are different languages, today I make a little typo in the following program but the program compiles fine on various C++ compilers (g++,clang,MSVC++)

Consider following program:

int main()
{
    int s[]={3,6,9,12,18};
    int* p=+s;  // Observe this strange looking initialization due to use of unary + operator
}

The above program compiles fine in C++ (See live demo here) but not in C (See live demo here.) My compiler ( gcc 4.8.1 ) gives me following error when I compile it as a C program.

[Error] wrong type argument to unary plus

What purpose the unary plus operator serves here? What it does exactly here? Why it is not allowed in C?

Solution

  • The section 6.5.3.3 of C99 states:

    1) The operand of the unary + or - operator shall have arithmetic type; ......

    2) The result of the unary + operator is the value of its (promoted) operand. The integer promotions are performed on the operand, and the result has the promoted type.

    Pointers or arrays are not an arithmetic type.