Please help... Global structures

This is a discussion on Please help... Global structures within the C Programming forums, part of the General Programming Boards category; Hi - I am quite new to this and not sure if I can do the below. Below is one ...

  1. #1
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    Please help... Global structures

    Hi - I am quite new to this and not sure if I can do the below. Below is one file in a multi-file program... basically the main program calls initialise() and then calls process_access().

    The arguments passed to process_access are fixed as is - but i need to be able to access the structures from all the fuctions without passing them. The members set correctly on initialisation but if i try to call them through the other functions they are all zero....

    This probably doesnt make much sense but if somebosy could help me out i would be really grateful... thanks.

    Code:
    typedef struct{
    
            int mem_blk;
            int cache_blk;
            int bank_num;
            int dirty;
            int valid;
    
    } Block_Struct;
    
    typedef struct {
    
            IndexFunc indexfunc_ptr;
            Block_Struct *blocks;
    
    } Bank_Struct;
    
    typedef struct {
    
            int size_blks;
            int blks_per_bank;
            int num_banks;
            Bank_Struct *banks;
    
    } Cache_Struct;
    
    Cache_Struct one_data;
    Cache_Struct one_inst;
    Cache_Struct two;
    
    void initialise_cache(CacheParams params, Cache_Struct cache);
    Block_Struct * find(Cache_Struct cache, int memory_address);
    
    
    
    void
    initialize(CacheParams l1_inst_params, CacheParams l1_data_params,
            CacheParams l2_params)
    {
    
            initialise_cache(l1_inst_params, one_inst);
            initialise_cache(l1_data_params, one_data);
            initialise_cache(l2_params, two);
    
    }
    
    
    
    void
    initialise_cache(CacheParams params, Cache_Struct cache){
    
            int i = 0;
    
            cache.num_banks = params.num_banks;
            cache.size_blks = params.block_size;
            cache.blks_per_bank = params.num_blocks_per_bank;
    
            cache.banks = malloc(sizeof(Bank_Struct)*(cache.num_banks));
    
            /* loops for each bank in the cache to initalise the blocks in the bank */
            for( i = 0; i < (cache.num_banks); i++ ){
    
                    int j;
    
                    cache.banks[i].indexfunc_ptr = params.index_func[i];
    
                    cache.banks[i].blocks =
                            malloc(sizeof(Block_Struct)*(cache.blks_per_bank));
    
                    for ( j = 0; j < cache.blks_per_bank; j++ ){
    
                            cache.banks[i].blocks[j].cache_blk = j;
                            cache.banks[i].blocks[j].bank_num = i;
                            cache.banks[i].blocks[j].dirty = 0;
                            cache.banks[i].blocks[j].valid = 0;
                    }
            }
    
    }
    
    Block_Struct *
    find(Cache_Struct cache, int memory_address){
    
            int i;
            int num_banks, blk_size;
            int blk_offset, mem_blk_number;
            int cache_blk;
    
            Block_Struct * blk_ptr;
    
            blk_size = cache.size_blks;
    
            blk_offset = memory_address % blk_size;
            mem_blk_number = memory_address / blk_size;
    
            for( i = 0; i < num_banks; i++ ){
    
                    cache_blk = cache.banks[i].indexfunc_ptr(mem_blk_number, cache.blks_per_bank);
    
                    blk_ptr = &(cache.banks[i].blocks[cache_blk]);
    
                    if ( (blk_ptr->mem_blk == mem_blk_number) && blk_ptr->valid )
                            return blk_ptr;
            }
    
            return NULL;
    
    }
    
    void
    process_access(AccessType access_type, int address, int access_size)
    {
    
            if( access_type == ACC_DATA_READ )
                   
                    find(one_data, address);
         
    }

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    It would make more sense to me if you posted a minimally compilable snippet that demonstrates the problem.
    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.*

  3. #3
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    My problem is...

    Sorry - basically this is my problem. Am i able to access the structures that 'structure' and 'stucture2' point to in other functions without passing to the function. I get a segmentation fault in line i=structure->info.....

    Code:
    typedef struct {
    
            int info1;
    
    } Second_Struct;
    
    typedef struct {
    
            int info;
            Second_Struct *second;
    
    } First_Struct;
    
    First_Struct *structure;
    First_Struct *structure2;
    
    int main(int argc, char **argv){
    
            initialise();
            access_structure();
            return 1;
    }
    
    void
    initialise(void)
    {
            initialise_structure(structure);
            initialise_structure(structure2);
    }
    
    void
    initialise_structure(First_Struct *i_structure){
    
            int i = 0;
            i_structure = malloc(sizeof(First_Struct));
            i_structure->info = 13;
            i_structure->second = malloc(sizeof(Second_Struct)*(6));
    
            for( i = 0; i < (6); i++ )
                    i_structure->second[i].info1 = i;
    
    }
    
    void
    access_structure(void)
    {
    
            int i;
        
            i = structure->info;
         
    }

  4. #4
    Just Lurking Dave_Sinkula's Avatar
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    Ah. If you want to modify a pointer passed into a function, you need to pass a pointer to it; i.e. a pointer to a pointer to your structure is necessary in order to malloc it in a called function and have the change persist in the calling code.

    [edit]Something like this:
    Code:
    #include <stdlib.h>
    
    typedef struct {
       int info1;
    } Second_Struct;
    
    typedef struct {
       int info;
       Second_Struct *second;
    } First_Struct;
    
    First_Struct *structure;
    First_Struct *structure2;
    
    void initialise_structure(First_Struct **i_structure)
    {
       int i = 0;
       *i_structure = malloc(sizeof(First_Struct));
       (*i_structure)->info = 13;
       (*i_structure)->second = malloc(sizeof(Second_Struct)*(6));
    
       for ( i = 0; i < (6); i++ )
       {
          (*i_structure)->second[i].info1 = i;
       }
    }
    
    void access_structure(void)
    {
       int i = structure->info;
    }
    
    void initialise(void)
    {
       initialise_structure(&structure);
       initialise_structure(&structure2);
    }
    
    int main(int argc, char **argv)
    {
       initialise();
       access_structure();
       return 0;
    }
    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
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    OK great, thanks.

    So if i pass a pointer to the pointer to the structure to initialise it - then I can access it in functions without passing it to those functions??

  6. #6
    Just Lurking Dave_Sinkula's Avatar
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    It seems like an odd mix of globals with passing parameters, but sure.
    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.*

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