How to Get the Length of File in C

How to get length of file in C

//===
int fileLen(FILE *fp)
{
    int nRet = -1;
    int nPosBak;

    nPosBak = ftell(fp);///< current position in file

    fseek(fp, 0, SEEK_END);
    nRet = ftell(fp);

    fseek(fp, nPosBak, SEEK_SET);///< write back position to file
    return nRet;
}

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