When I write C I tend to always return any error code on the stack and pass the pointer to where I want the result to go. Makes managing memory easier. The owner gets to allocate.

Example:

  #define E_DIVZERO -100
  int divide(float a, float b, float *result) { 
      if (b == 0.0) return E_DIVZERO;
      *result = a / b;
  }