Thread: #typedef question

I've found a need to reverse the endianness of integer data read from some files I'm working with. So I wrote the following:

Code:

typedef unsigned int uint;
typedef unsigned char byte;
uint reversendian(uint i)
  {
     union { uint i; byte b[4]; } in, out;
     int j;
     in.i=i; 
     for (j=0; j<4; j++)
       {
         out.b[3-j]=in.b[j];
       }
     return out.i;
  }

I say "uint" and "byte" because I get tired of typing "unsigned int" and "unsigned char" all the time. These typedefs are actually in the header file for the functions in my own library.

This function works for my purposes. But the problem, of course, is that it is not portable, because it assumes a 4-byte size for int or unsigned int. What can I use for the type of data of the parameter, returned value, and innards such that it will serve for either signed or unsigned four-byte integers, but a compiler will reject attempts to use it for other sizes?

uint32_t in stdint.h if your compiler is at least C99 will remove some variability.

But you won't be able to stop people calling it with shorter types because of default promotion rules.

In your particular case though, you might not need to be fixated on requiring a 4-byte unsigned int: you could replace both uses of 4 with sizeof(uint) and the use of 3 with sizeof(uint)-1. This way your code will work even if unsigned int has a different number of bytes.