Answers below
Joerg Schilling wrote:
Steve Bennett <[EMAIL PROTECTED]> wrote:
#include <stdio.h>
struct test1
{
char blerg[1];
char type[4];
char flibble[3];
char more[2];
} __attribute__((packed));
_Pragma("pack(1)") struct test2
{
char blerg[1];
char type[4];
char flibble[3];
char more[2];
};
int main (int argc, char **argv)
{
printf("sizeof(test1) is %d\n", sizeof(struct test1));
printf("sizeof(test2) is %d\n", sizeof(struct test2));
return 0;
}
What does this print?
sizeof(test1) is 10
sizeof(test2) is 12
So _Pragma() works the same way as #pragma.
What do you get from:
printf("vers %d\n", __STDC_VERSION__):
test2.c: In function 'main':
test2.c:5: error: '__STDC_VERSION__' undeclared (first use in this function)
test2.c:5: error: (Each undeclared identifier is reported only once
test2.c:5: error: for each function it appears in.)
test2.c:5: error: syntax error before ':' token
This is interesting! I tought that GCC is a bit closer to the standard.....
Ah, well. You probably want gcc in c99 mode!
I'll try again with -std=c99
[EMAIL PROTECTED]:/share/tmp/mkisofstest$ gcc -std=c99 test2.c -o test2
[EMAIL PROTECTED]:/share/tmp/mkisofstest$ ./test2
vers 199901
Better.
what do you get from:
struct test1
{
char blerg[1];
char type[4];
char flibble[3];
char more[2];
char dummy[];
};
int main (int argc, char **argv)
{
printf("sizeof(test1) is %d\n", sizeof(struct test1));
return 0;
}
sizeof(test1) is 12
This is really bad!
After reading the C-99 Standard, it turned out that the last method
is the "official" way to prevent tail padding of structures.
Could you please run the last test again but use:
#pragma pack(1)
struct test1
{
char blerg[1];
char type[4];
char flibble[3];
char more[2];
char dummy[];
};
sizeof(test1) is 12
And just in case you are wondering, I ran all those previous tests again
with -std=c99 with exactly the same results.
Cheers,
Steve
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