Difference between "3" and '3' in C

Question

I tried to run the following program in C and got some output. Can you help me out why???

#include<stdio.h>

int main()
{
  char x='A';
  printf("%d%d%d",sizeof("3"),sizeof('3'),sizeof(3));
  return 0;
}

The output received is 2 4 4 using gcc in ubuntu 11.04 32 bit.

Similarly in other program:-

#include<stdio.h>

int main()
{
  char x='A';
  printf("%d%d",sizeof('A'),sizeof(x));
  return 0;
}

The output received is 4 1 using GCC in ubuntu 11.04 32 bit.

Can you help me out why the output is this way???

Answer 1

In C, char literals are of integer type, so sizeof('3') == sizeof(int). See this C FAQ for details.

This is one of the areas where C and C++ differ (in C++ sizeof('3') is 1).

Actually, correcting my previous assertion, sizeof("3") will yield 2 because "3" is treated as a 2-element character array.

6.3.2.1/3

Except when it is the operand of the sizeof operator or the unary & operator, or is a string literal used to initialize an array, an expression that has type ‘‘array of type’’ is converted to an expression with type ‘‘pointer to type’’ that points to the initial element of the array object and is not an lvalue.