【C】Pointer (11) You Can Define Same Tag Name at Most Once
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Where two declarations that use the same tag declare the same type, they shall both use the same choice of struct, union, or enum.
As far as I confirm by writing codes, in the end, I think I can declare same tag name only at once.
Here is the code. Using same tag name in union and structure. This will be error. uniton-structure.c
#include <stdio.h>
int main (void ){
union test {
char c;
int i;
} test1;
struct test {
char c;
int i;
} test1;
test1.c = "A";
printf("test1.c = %c \n", test1.c);
printf("test1.i = %i \n", test1.i);
test1.i = 100 ;
printf("test1.c = %c \n", test1.c);
printf("test1.i = %i \n", test1.i);
return 0;
}Compile result of union-structure.c
$ gcc union_structure.c
union_structure.c: In function ‘main’:
union_structure.c:10:9: error: ‘test’ defined as wrong kind of tag
struct test {
^
union_structure.c:13:4: error: conflicting types for ‘test1’
} test1;
^
union_structure.c:8:4: note: previous declaration of ‘test1’ was here
} test1;
^
union_structure.c:15:10: warning: assignment makes integer from pointer without a cast [enabled by default]
test1.c = "A";
^Different tag name for union and structure union_structure2.c
#include <stdio.h>
int main (void ){
struct test2 {
char c;
int i;
} st;
union test1 {
char c;
int i;
} uni;
st.c = 'A';
uni.c = 'A';
st.i = 100 ;
uni.i = 100 ;
printf("st.c = %d \n", st.c);
printf("st.i = %d \n", st.i);
printf("uni.c = %d \n", uni.c);
printf("uni.i = %d \n", uni.i);
st.i = 260 ;
uni.i = 260 ;
printf("st.c = %d \n", st.c);
printf("st.i = %d \n", st.i);
printf("uni.c = %d \n", uni.c);
printf("uni.i = %d \n", uni.i);
return 0;
}Compile result and execution result of union_structure2.c
$ gcc union_structure2.c
$ ./a.out
st.c = 65
st.i = 100
uni.c = 100
uni.i = 100
st.c = 65
st.i = 260
uni.c = 4
uni.i = 260 That’s all for this time.
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