bit packed structs

/* 17oct07 John Pfeiffer packing bits in structs example

according to msdos prompt dir unpacked.txt is 24 bytes, packed.txt is 8 bytes 
...of course with gcc packed becomes 4 bytes...
compiled with tcc... allowed me all sorts of irregular coding =)
compiled with gcc we had to clean up our malloc (add stdlib.h) and
use pointers (correct objects! :)

should use calloc? - for inialized to 0's? void* calloc(size_t elems, size_t bytes)
realloc for shrinking? - but if a new temp variable does not get the return value
then you could cause a memory leak...

NOTE: malloc needs to be error checked, if no free mem then returns NULL ptr...
Dangling pointer = Do not use the pointer after it has been freed, especially
do not "double free", set the ptr to NULL after freeing...
*/

#include <stdio.h>
#include <stdlib.h>

struct char_and_flags_unpacked
{
        char character;
        int a;
        int b;
        int c;
        int d;
        int e;
};

typedef struct 
{
        char character;
        int a:1;
        int b:1;
        int c:1;
        int d:1;
        int e:1;
} char_and_flags_packed;

int main(int argc, char *argv[])
{
        struct char_and_flags_unpacked* unpacked;
        char_and_flags_packed* packed;
        char dos_cmd[30];

        FILE* fptru = fopen("unpacked.txt","w");
        FILE* fptrp = fopen("packed.txt","w");

        if( fptru == NULL )
        {   printf("File Error unpacked.txt");  exit(1);    }

        if( fptrp == NULL )
        {   printf("File Error packed.txt");    exit(1);    }

        unpacked = (struct char_and_flags_unpacked*) malloc( sizeof( struct char_and_flags_unpacked ) );
        if (unpacked == NULL)
        {   printf("Memory Error unpacked struct malloc");  exit(1);    }

        packed = (char_and_flags_packed*) malloc( sizeof(char_and_flags_packed) );
        if (packed == NULL)
        {   printf("Memory Error packed struct malloc");    exit(1);    }

        (*unpacked).character = 'a';
        (*unpacked).a = 1;
        (*unpacked).b = 1;
        (*unpacked).c = 1;
        (*unpacked).d = 1;
        unpacked -> e = 1;

        packed -> character = 'a';
        packed ->a = 1;
        packed ->b = 1;
        packed ->c = 1;
        packed ->d = 1;
        packed ->e = 1;

        fwrite( (char*) &unpacked, 1 , sizeof( struct char_and_flags_unpacked ), fptru ); 
        fwrite( (char*) &packed, 1 , sizeof( char_and_flags_packed ), fptrp );

        /* fflush( fptru);  */

        printf("This might print out the directory where the packed files are...\n");
        strcpy(dos_cmd, "dir *.txt");
        system(dos_cmd);


        free(unpacked);
        free(packed);
        unpacked = NULL;
        packed = NULL;

        fclose(fptru);
        fclose(fptrp);

        return 0;
}