Question

Using the following code to write to a file

int main(int argc, char * argv[])
{
    uint32_t pattern1, pattern2;
    int i, times;
    sscanf("ae75db0f", "%x", &pattern1); 
    sscanf("518a24f0", "%x", &pattern2);
    FILE * outFile = fopen(argv[1],"wb");
    printf ("Pattern 1: %0x \nPattern 2: %0x \n", pattern1, pattern2);

    times = 524288; // Write out 4 mB of data

    for (i = 0; i < times; i++) {
        fwrite(&pattern1, 4, 1, outFile);
        fwrite(&pattern2, 4, 1, outFile);
    }
    fclose (outFile);
}

On the command line I do xxd file | less

00018c0: f024 8a51 0fdb 75ae f024 8a51 0fdb 75ae  .$.Q..u..$.Q..u.
00018d0: f024 8a51 0fdb 75ae f024 8a51 0fdb 75ae  .$.Q..u..$.Q..u.
00018e0: f024 8a51 0fdb 75ae f024 8a51 0fdb 75ae  .$.Q..u..$.Q..u.
00018f0: f024 8a51 0fdb 75ae f024 8a51 0fdb 75ae  .$.Q..u..$.Q..u.

It’s not showing the “correct” values that were supposed to be written to the file itself.

Answer 1

Welcome to the world of the endianness:

http://en.wikipedia.org/wiki/Endianness

x86/x64 architectures (like most architectures nowadays) are little endian: it means multi-bytes values are stored in memory with the Least Significant Bytes first (low memory address).