why the endian of write Struct in file is different with the Struct in memory?

Question

I try to write a struct into file, then i found the endian of that is differet with the endian in the memory.

some test code:

void show_hex(unsigned char *p, int n)
{

    for (int i=0; i<n;i++){
        printf("%02X ",p[i]);
    }

}

int main()
{
    FILE *fp = fopen("as","w");
    struct X{
        int x,y;
    };
    struct X *p = malloc( sizeof(struct X));
    p->x = 0xFFEECCAA;
    p->y = 0xFFAADD;
    show_hex((unsigned char *) p, sizeof(struct X));
    fwrite(p, sizeof(struct X), 1, fp);
    fclose(fp);

    int f = open("as2",O_WRONLY);
    write(f, p, sizeof(struct X));
    close(f);
    return 0;
}

the problem out put : AA CC EE FF DD AA FF 00 //i know that is the little endian

tyw@um08:~/pro|master⚡ ⇒  hexdump as
0000000 ccaa ffee aadd 00ff                    
0000008
tyw@um08:~/pro|master⚡ ⇒  hexdump as2
0000000 ccaa ffee aadd 00ff                    
0000008

So the endin is different.

You could have tested this by using echo 1234 | hexdump instead of assuming the endian was wrong. When all else fails, man hexdump. — paddy
– paddy, Commented Mar 14, 2013 at 23:12

Ben Jackson · Accepted Answer · 2013-03-14 23:06:00Z

6

The endianness of the file isn't different than the memory. The default behavior of hexdump is to print the values as 16-bit shorts. What you are seeing is a different interpretation of the memory. Try hexdump -C

answered Mar 14, 2013 at 23:06

Ben Jackson

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