PRB: Initializing Non-Primary Union Element Produces Errors (39910)

MORE INFORMATION

Example1.c, in the sample code below, fails compilation with one C2078 error and three C4047 warnings. The error is generated because only one union element may be initialized (the first) and by the time the compiler processes the "{ch1,ch2,ch3,ch4}" initialization, it has already filled element one. The warnings are generated because the compiler expects to be initializing "union TEST tsty" with integer values, but it is finding char* (character pointers) instead.

Example2.c compiles but produces a C4133 warning. The compiler expects to initialize "union ONION anONION" with an integer pointer but finds a float pointer instead. Although, this situation is not serious enough to prohibit compilation, it does indicate that there may be a problem.

Sample Code

/* Example1.c
 *
 * Compile options needed: none
 */ 

union TEST
{
    struct
    {
      int a;
      int b;
      int c;
    } one;             /* union element #1 */ 
    struct
    {
      char *ptr1;
      char *ptr2;
      char *ptr3;
      char *ptr4;
    } two;             /* union element #2 */ 
} u;

char ch1[10], ch2[10], ch3[10], ch4[10];

union TEST test ={ {1,2,3},                /* initialize element #1 */ 
                   {ch1,ch2,ch3,ch4} };    /* generates error C2078 */ 

void main(void)
{
   union TEST tsty ={ {ch1,ch2,ch3,ch4} }; /* generates 3 C4047
                                              warnings */ 
}

-------------
/* Example2.c
 *
 * Compile options needed: /c
 */ 

union  ONION  { int *iptr; float *fptr; };
float sam = 3.141592;
union ONION anONION = { &sam };  /* generates warning C4133 */