INFO: sizeof(char Expression) Same as sizeof(int)

• The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5 - Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 4.0, 5.0

SUMMARY

In Microsoft C/C++, expressions involving variables of type "char" are promoted to type "int".

MORE INFORMATION

This is ANSI-specified behavior. Below is Section 3.3.7 from the ANSI specifications, which details the semantics of the shift operator:

   Semantics
      The integral promotions are performed on each of the operands.
      The type of the result is that of the promoted left operand. If
      the value of the right operand is negative or is greater than or
      equal to the width in bits of the promoted left operand, the
      behavior is undefined.

The ANSI-specified semantics of all operators specify promotion from char to int, so the size of any char expression will be the sizeof int. This was also the case for Kernighan and Ritchie (K & R) C.

The sizes of the int and long expressions stay the same because no promotion takes place.

Note that if int is the same size as long rather than short in this implementation, the sizeof both a short expression and a char expression will be 4, as will be the sizeof both an int and a long expression.

Sample Code

   /* Compile options needed: none
   */

   #include <stdio.h>

   void main(void)
   {
      short si;
      long li;
      char sc;
      unsigned char uc;

      printf("Signed char width: %d\n",
              sizeof((char)(sc<<1)));          // 1 byte

      printf("Signed char width: %d\n",
              sizeof(sc<<1));                 // 2 bytes

      printf("Unsigned char width: %d\n",
              sizeof((unsigned char)uc<<1));  // 2 bytes

      printf("Unsigned char width: %d\n",
              sizeof(uc<<1));                 // 2 bytes

      printf("Short width: %d\n",
              sizeof(si<<1));                 // 2 bytes

      printf("Long width: %d\n",
              sizeof(li<<1));                 // 4 bytes
   }