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File CRC

Posted on 2004-11-05
Medium Priority
Last Modified: 2010-04-01
How would one go about returning the CRC of a file given the name stored in a char*, in non-MFC C++ or C. I've been trying different things but just can't get it to work.
Question by:State
  • 2

Accepted Solution

mnashadka earned 450 total points
ID: 12512807
You should check out the Boost library's CRC.  The documentation can be found at: http://www.boost.org/libs/crc/crc.html .  You just need to read the file into a buffer and call the process_bytes and checksum functions.  This header file should be able to be included in any relatively standard-conforming C++ compiler.
LVL 55

Expert Comment

by:Jaime Olivares
ID: 12513851
Some C code:

DWORD get_crc_32(char *filename)
    static unsigned long crc_table[256];
    static bool generated = false;
    unsigned long crc;
    FILE *fp;
    int c;
    if (!generated) {
        unsigned long crc, p;
        int    i, j;
        for (i = 0; i < 256; i++) {
            crc = i;
            for (j = 8; j > 0; j--) {
                if (crc & 1)
                    crc = (crc >> 1) ^ 0xEDB88320L;
                    crc >>= 1;
            crc_table[i] = crc;
        generated = true;

    if ( !(fp=fopen(filename, "rb")))
        return NULL;                               <------------------------ When error occurs, return 0

    crc = 0xFFFFFFFF;
    while ((c = getc(fp)) != EOF)
        crc = (crc>>8) ^ crc_table[ (crc^c) & 0xFF ];
    crc ^= 0xFFFFFFFF;


    return CRC;
LVL 55

Expert Comment

by:Jaime Olivares
ID: 12692179
Have provided a functions that does what author resquested, waiting for some feeback...

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