run-time var initialization

This is a discussion on run-time var initialization within the C Programming forums, part of the General Programming Boards category; In plain C, when initializing a matrix you can do it: int m[2][2] = { {2,3} , {3,4} }; but ...

  1. #1
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    run-time var initialization

    In plain C, when initializing a matrix you can do it:
    int m[2][2] = { {2,3} , {3,4} };
    but I am trying to do it at run time:


    Code:
    int F[5][8];
    
    int main()
    {
    	int x= 1;
    	F[x] = {-6, -3, 0, 4, 8, 6, 2, -4 };
    	int x= 2;
    	F[x] = {-7, -3, 0, 5, 8, 6, 2, -8 };
            .....
        return 0;
    }
    And I get compiling errors. It looks like this way is not allowed.

    Is there any way to inialize a matriz in bulk, so that there is no need to initialize values one by one.

    thanks

  2. #2
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    int m[2][2] = { {2,3} , {3,4} };
    It's already initialization in bulk.

  3. #3
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    Quote Originally Posted by Bayint Naung View Post
    int m[2][2] = { {2,3} , {3,4} };
    It's already initialization in bulk.
    That is not what I want. suppose I want to initialize it depending on a var:

    Code:
    int F[5][8];
    
    int main()
    {
    	if (z == 18) {
    	    F[1] = {-6, -3, 0, 4, 8, 6, 2, -4 };
            } else {
    	    F[1] = {-7, -3, 0, 5, 8, 6, 2, -8 };
            }
            .....
        return 0;
    }
    I can not do this also. any idea or I must do it value by value?

  4. #4
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    Code:
    	
            if (z == 18) {
             int temp[] =  {-6, -3, 0, 4, 8, 6, 2, -4 };   
             /* of course you can use 
            #define  INIT_ARRAY  { -6, -3,0,blah}  int temp[] = INIT_ARRAY;  
             */
                 // copy 
                memcpy(f[1],temp,sizeof(temp));
            } else {
                int temp[] = {-7, -3, 0, 5, 8, 6, 2, -8 };
               // similar
            }
    Or use variadic macro. Example (Not suppose to be perfect
    Code:
    #define INIT_ARRAY(array,type,...)    \
    do {                                                                    \
          memcpy(array,  ( type [ sizeof(array)/sizeof(array[0]) ]) { __VA_ARGS__ }, sizeof(array) );   \
    } while(0)
    INIT_ARRAY(f[1],int, 3,4,5 );     // eg usage
     } while(0)
    Last edited by Bayint Naung; 06-23-2010 at 04:19 AM.

  5. #5
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    macro? memcpy? stay away

    just make a new array and copy over the contents

    Code:
            if (z == 18) {
                        int temp[] = {-6, -3, 0, 4, 8, 6, 2, -4 };
    	    for(...) {
                            F[1][i] = temp[i]
                        }
            } else {
    just some general advice:
    when writing a program, the first thing you should do is get something that works and is correct. then go back and do whatever you feel is required. i think you knew exactly how to get around this problem by using a temp array and i dont think you should have spent any more than a few seconds trying to think of better method. the temp array solution was simple, obvious and clear.

    its like when you are writing an essay at home. the first thing you should do is write it all out. then you should go and choose fonts, choose header styles, colors, pictures, etc. but only after youve finished

    and use spaces, not tabs. if you must use tabs, then dont mix and match with spaces.

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