C Programming - Malloc Structs and undefined arrays

Question

I am writing a program in C and I am trying to create these structs. I have three of them:

1. the first consisting of 2 ints and 2 chars,
2. the second consisting of an int and an undefined array of pointers to the first one,
3. and a third which contains 4 longs and 2 ints along with an undefined array of pointers to the second.

I am having trouble I believe with memory allocation for these structs when instantiated. Does anyone know what I am doing wrong (code below). Cache_Simulator is the main class and uses the others. Any help appreciated.

Directory_block.c

#include <stdio.h>
#include <stdlib.h>
#include "Directory_Block.h"
/* Created September, 15th, 2010;
 *
 *             Author: TJ, Cory
 */

 char containsData(directory_block* checkMe){
     return checkMe->valid;
 }
 void setValidOn(directory_block* checkMe){
     checkMe->valid = 1;
 }
 void setValidOff(directory_block* checkMe){
     checkMe->valid = 0;
 }
 char isOlder(directory_block* checkMe, int currentOldest){
    if(currentOldest < checkMe->LRU){
         return 1;
      }
     else{
         return 0;
     }
 }
 void setTag(directory_block* setMe, int tag){
     setMe->tag = tag;
 }
 char matchesTag(directory_block* checkMe, int theirTag){
     if(checkMe->tag == theirTag){
         return 1;
     }
     else{
         return 0;
     }
 }
 void incrementLRU(directory_block* incrementMe){
    incrementMe->LRU++;
 }

 void setLRU(directory_block* editMe, int LRUVal){
     editMe->LRU = LRUVal;
 }

cache_set* createSet(int setNumber,int numberOfBlocks,int printDetails){
     cache_set* newSet = malloc(sizeof(cache_set) + sizeof(directory_block)*numberOfBlocks);
 newSet->setNumber = setNumber;
 printf("Making Set %d\n",newSet->setNumber);
 int i = 0;
 for(; i < numberOfBlocks;i++)
 {
     printf("\tMaking Block #%d  ",i);
     if((i%4)==0&&i!=0)
     {
         printf("\n");
     }
     directory_block* block = malloc(sizeof(directory_block));
     newSet->blocks[i] = block;
     setValidOff(newSet->blocks[i]);
     setTag(newSet->blocks[i],setNumber);
     setLRU(newSet->blocks[i],-1);
     if(printDetails == 1)
     {
         printf("\tAddress %d\n",(int)newSet->blocks[i]);
         printf("\t\tValid=%d\n\t\tLRU=%d\n\t\tTag=%d\n",newSet->blocks[i]->valid
                 ,newSet->blocks[i]->LRU,newSet->blocks[i]->tag);
     }
 }
 printf("\n");
 return newSet;

 }

Directory_block.h

#ifndef DIRECTORY_BLOCK_H_
#define DIRECTORY_BLOCK_H_
#include "Directory_Block.h"
struct directory_block;
struct set;
struct cache;

typedef struct{
  int tag;
  int LRU;
  char valid;
  char offset;
}directory_block;

typedef struct{
int setNumber;
directory_block* blocks[];
}cache_set;

typedef struct{
int numberOfSets;
int linesPerSet;
long hits;
long misses;
long unknownAccesses;
long flushes;
cache_set* sets[];
}cache;


/*
 * params: checkMe - the line of the cache that we are checking
 * return: true = valid == 1; false valid == 0
 */
char containsData(directory_block* checkMe);
/*
 * functions: to set the valid bit to 1
 */
void setValidOn(directory_block* checkMe);
/*
 * functions: to set the valid bit to 0
 */
void setValidOff(directory_block* checkMe);
/*
 * params: currentOldest - the current oldest in directory_block*
 * return: the oldest current directory_block*
 */
char isOlder(directory_block* checkMe, int currentOldest);
/*
 * params: theirTag - the tag that is in the directory_block*
 * return: 0 if false; 1 is true
 */
char matchesTag(directory_block* checkMe, int theirTag);
/*
 * function: increments the value of the LRU in the block
 */
void incrementLRU(directory_block* incrementMe);
void setTag(directory_block* setMe, int tag);
/*
 * param: LRUVal - value to set to LRU to (negative means hasn't been used)
 */
void setLRU(directory_block* editMe,int LRUVal);
/*
 * param: numberOfBlocks number of blocks per set
 * creates a set and instantiates all directory blocks;
 * param: setNumber number of this set in the cache
 */
cache_set* createSet(int setNumber,int numberOfBlocks,int details);

#endif /* DIRECTORY_BLOCK_H_ */

Cache.c

#include "Directory_Block.h"
#include <stdio.h>
#include <stdlib.h>

directory_block* findLRU(cache* checkMe,int index){
int age;
age = 0;
int i = 0;
int oldest = 0;
for(; i < checkMe->numberOfSets;i++)
{
    if(isOlder(checkMe->sets[i]->blocks[index],age) == 1)
    {
        oldest = i;
        age = checkMe->sets[i]->blocks[index]->LRU;
    }
}
return checkMe->sets[i]->blocks[i];
}

int readInAddress(cache checkMe,char fileName[]){

return 0;
}

cache *makeCache(int numberOfLines,int numberOfSets,int details){

cache* returnMe = (cache*)malloc(sizeof(cache) + sizeof(int)*numberOfSets);
returnMe->numberOfSets = numberOfSets;
returnMe->linesPerSet = numberOfLines;
printf("Making Cache\n");
int i=1;
for(; i < returnMe->numberOfSets;i++){
    returnMe->sets[i] = createSet(i,returnMe->linesPerSet,details);
}
return returnMe;
}

void writeToCache(cache *addToMe,int address,int tag,int offset)
{
directory_block* LRUblock = findLRU(addToMe,address);
LRUblock->LRU = 0;
LRUblock->tag = tag;
LRUblock->valid = 1;
LRUblock->offset = offset;
}

char processAddress(cache checkMe,int address){

 return 0;
}

void reportCacheStatus(cache *reportMe){
int i = 0;
int j = 0;

for(;i < reportMe->numberOfSets;i++)
{

    printf("Set #%d\n",i);
    for(j=0;j < reportMe->linesPerSet;j++)
    {
        printf("\tBlock #%d - Tag=%d  Valid=%d  LRU=%d Offset=%d\n",j,reportMe->sets[i]->blocks[j]->tag
                ,reportMe->sets[i]->blocks[j]->valid,reportMe->sets[i]->blocks[j]->LRU
                ,reportMe->sets[i]->blocks[j]->offset);
    }
}

}

Cache.h

#include "Set.h"
#ifndef CACHE_H_
#define CACHE_H_

/*
 * params: checkMe - cache which that we will look for LRU at
 *            index - line index which we will check for LRU in all sets
 * return: setIndex - of the LRU block
 * function - iterates through sets and compares LRU value of directory_block at given
 *               index for each set.
 *
     */
int findLRU(cache checkMe,int index);

    /*
 * params: char [] - Name of File to read
 * return address struct contains access type and parsed address
    */
int readInAddress(cache checkMe,char[]);

/*
 *params: int cacheSize total bytes in cache, int linesPerSet number of blocks per set
 *params: int lineSize number of bytes per line
 * return int [] pointer with # of fields
 * (DEFINE FIELDS)
 */
cache* makeCache(int numberOfLines,int numberOfSets,int details);

/*
 * params: int address - perform cpu call for that address and see if there is a
 *  hit or miss or unknown access type - Update stats
 */
char processAddress(cache checkMe,int address);

void writeToCache(cache *addToMe,int address);

/*
 *Prints out display of information
 *For passes cache
 *Ex.
 *    INSERT EXAMPLE LINE
 */
void reportCacheStatus(cache* reportMe,int numberOfSets,int blocksPerSet);


#endif     /* CACHE_H_     */

Cache_simulator.c

#include <stdio.h>
#include <stdlib.h>
#include "fileParser.h"
#include "Directory_Block.h"
#include "Cache.h"
void setupCache(int details);
void performTrace(void);
void report(void);

int main(void)
{
printf("The Cache Simulator:\n\tJonathan Katon\n\tCory Brett\n\tThomas Pavlu\n");
setupCache(1);
//performTrace();
report();
return 0;
}

void setupCache(int details)
{
int numberOfLines = 1024/1;
int numberOfSets = numberOfLines/4;
numberOfLines = numberOfLines/numberOfSets;
printf("Number of Sets %d \nNumber of Lines Per Set %d\n",numberOfSets,numberOfLines);
printf("Cache Size %d,Cache_Set Size %d,Directory_block Size %d",sizeof(cache),sizeof(cache_set),sizeof(directory_block));
cache *instructionCache = makeCache(numberOfLines,numberOfSets,details);
//writeToCache(instructionCache,0);
reportCacheStatus(instructionCache,numberOfSets,numberOfLines);

}

void performTrace(void)
{
FILE* trace;
trace = fopen("trace.txt","r");
readNextMemoryAccess(trace);
}

void report(void)
{ // T.B.D
}

---

From an 'answer' by the OP about the question:

This was my attempt to try and fix a problem I was having with the memory at least i think I was. When I do a sizeof(cache_set) only it only returns a size large enough for everything but the array of pointers. This makes sense because the array isn't finite my question is how do I get around this issue? Any suggestions. Oh, and by the way, thanks for taking at look at this.

Answer 1

in Directory_block.c

cache_set* newSet = malloc(sizeof(cache_set) + sizeof(directory_block)*numberOfBlocks);

newSet is a pointer with space for:

1. 1 cache_set: ok
2. numberOfBlocks directory_blocks: huh?

This is wrong: cache_sets do not have directory_blocks in them; they have pointers to directory_blocks

typedef struct{
int setNumber;
directory_block* blocks[];
}cache_set;

I'd pay great attention to your type structure. Do you really need an array of pointers to directory_blocks inside cache_sets? If you do, the typedef is ok; if you don't, it's (probably) the code that's ok ... but, anyway, ... the structure and the malloc don't match.

---

Edit use the flexible array member

Suppose we have a struct with a flexible array member

struct Example {
    int value;
    double fam[]; /* fam is the flexible array, of doubles */
};

and now we want to use a variable of type struct Example with space for 100 doubles:

struct Example *example;
example = malloc(sizeof *example + 100 * sizeof *example->fam);
if (example) {
    /* use example, eg: */
    example->fam[42] = 3.14159265;
    /* and remember to free the allocated object when done */
    free(example);
}