Pointer to a typedef struct

This is a discussion on Pointer to a typedef struct within the C Programming forums, part of the General Programming Boards category; Hi, Please help me with this C syntax. I get a incompatible type warning with this: typedef struct{ unsigned char ...

  1. #1
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    Pointer to a typedef struct

    Hi,

    Please help me with this C syntax. I get a incompatible type warning with this:

    typedef struct{
    unsigned char a;
    unsigned char b;
    unsigned char c;
    } TEST;

    void main(void)
    {
    unsigned char *pointer;
    TEST Test;

    pointer = &Test;
    }

    What I tried to do there is to get the address of "Test".
    Thanks!
    James

  2. #2
    C++まいる!Cをこわせ!
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    TEST Test;
    TEST* pointer = &Test;
    Types must match, or you must use a cast (bad practice unless you know what you're doing).

    Also, http://cboard.cprogramming.com/dos-p...ead-first.html
    And of course, http://cpwiki.sourceforge.net/void_main
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  3. #3
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    Thank you for your quick reply. I run into another incompatible type:

    Code:
    #define Element_A_Offset 0
    #define Element_B_Offset 1
    #define Element_C_Offset 2
    #define Element_D_Offset 3
    
    typedef struct{
      unsigned char a;
      unsigned char b;
      unsigned char c;
      unsigned char d;
    } TEST;
    
    TEST Array[2];
    
    //----------------------
    // Get X element of an Y array index
    //----------------------
    unsigned char Get_Element(unsigned char Array_Index, unsigned char Element_X_Offset)
    {
      TEST *pointer;
      unsigned char IndexOffset, Val;
      
      pointer = &Array[0];                                  // get address of array
      IndexOffset = Array_Index << 2;                       // 4 byte each
      Val = *(pointer + IndexOffset + Element_X_Offset);    // get element X of Array_Index
      *(pointer + IndexOffset + Element_X_Offset) = 0xAA;   // set element X of Array_Index
      
      return Val;
    }
    //------------
    
    void main (void)
    {
      unsigned char Value;
      
      Value = Get_Element(1, Element_B_Offset);
    }
    Thank you very much in advance!
    James

  4. #4
    C++まいる!Cをこわせ!
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    pointer is a pointer to a TEST. Val is an unsigned character.
    You still haven't addressed the void main problem.
    Perhaps you should describe what you are trying to do. This code will most likely fail in a most horribly manner.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  5. #5
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    Hi,

    The function "Get_Element" is supposed to return the value of an element of a specific index of the array.

    For example, the function call:

    Value = Get_Element(1, Element_B_Offset);

    The returned value "Value" should be the value of element b of the second structure in the array "Array".

    Hope I didn't confuse you more...
    James

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    I think our question is, why are you using techniques (char * as a generic type, using addresses to get at parts of a struct) that are considered bad form (and have been for a long time)?

    After all, if you want the value of element b of the second structure in the array "Array", why not just type
    Code:
    Array[1].b
    ?

  7. #7
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    I am writing code for a microcontroller and I want it to execute as fast as possible. Using "Array[1].b" would work perfectly, but it would involve some mulitply operations when the code compiles. Multiply/divide operation in a microcontroller takes many cycles.

    I wanted to speed it up by just use shifting, add and, subtract operations, which usually take only few cycles to complete.

    James

  8. #8
    C++まいる!Cをこわせ!
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    You are sure the compiler won't optimize this for you?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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