Thread: Copy structure elements into byte array

  1. #1
    Registered User
    Join Date
    May 2003

    Copy structure elements into byte array

    Can somebody please tell me how go about copying the elements of a structure into a byte array. Your assistance is greatly appreciated.

    Thanks in advance!

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    Do you care about copying the padding bytes which may be between members of the structure or not?

    Further, if you intend to send this array of bytes to some external machine, do you care about fixing things like the endian-ness of data types?

    Does your structure contain pointers, and do you want to intelligently do the "right thing" with the data which is being pointed to?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
    Registered User
    Join Date
    May 2003

    byte array

    I do not want the padding bytes.

    I'm not worried about endian-ness.

    There are no pointers in the structure.

    I'm mainly just looking for a C syntax example.

  4. #4
    Just Lurking Dave_Sinkula's Avatar
    Join Date
    Oct 2002
    One way would be to memcpy member by member.
    #include <stdio.h>
    #include <string.h>
    struct dumb
       char   broiled;
       short  circuit;
       long   johns;
       double entendre;
    size_t serialize(unsigned char *dst, const struct dumb *object)
       size_t i = 0;
       memcpy(&dst[i], &object->broiled, sizeof object->broiled);
       i += sizeof object->broiled;
       memcpy(&dst[i], &object->circuit, sizeof object->circuit);
       i += sizeof object->circuit;
       memcpy(&dst[i], &object->johns, sizeof object->johns);
       i += sizeof object->johns;
       memcpy(&dst[i], &object->entendre, sizeof object->entendre);
       i += sizeof object->entendre;
       return i;
    void showbytes(const void *object, size_t size)
       const unsigned char *byte;
       for ( byte = object; size--; ++byte )
          printf("%02X", *byte);
    int main()
       int member;
       struct dumb by[sizeof member] =
          { 'A', 0x1234, 0x12345678, 123.456},
       unsigned char buffer [ sizeof by[0] ];
       showbytes(buffer, serialize(buffer, by));
       return 0;
    /* my output
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  5. #5
    Registered User
    Join Date
    May 2003


    Thanks Dave!

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