Dynamic Array

This is a discussion on Dynamic Array within the C Programming forums, part of the General Programming Boards category; In this part of my program i -obviously- want to create a dynamic array. But somewhere there is a problem(the ...

  1. #1
    Registered User
    Join Date
    Jun 2007
    Posts
    11

    Dynamic Array

    In this part of my program i -obviously- want to create a dynamic array.
    But somewhere there is a problem(the array is allocacated but not returned), can anyone help me, is there any problem with the pointers?
    I have a warning into the main that A hasn't been initialized


    Code:
    #include<stdio.h>
    #include<time.h>
    #include<stdlib.h>
    
    int FillStruct(int A[]);
    
    int main(void){
    	
    	int megethos,*A,epilogi;
    	srand(time(NULL));
    	
    	do{
    		printf("--------------------------\n       Main Menu\n--------------------------\n");
    		printf("Give a choice: ");
    		scanf("%d",&epilogi);
    		switch (epilogi) {
    		case 1:
    			megethos=FillStruct(A);
    			break;
    	.
    	.
    	.
    	.
    	.
            }
    	return 0;
    }
    
    int FillStruct(int A[])
    {
    	int type,zevgaria,thesi,temp,i,megethos;
    	printf("Please give the length of the struct:");
    	scanf("%d",&megethos);
    
    	A=(int*)calloc(megethos,sizeof(int));
    	if (A==NULL){
    		printf("ALLOCATING MEMMORY ERROR");
    		exit(1);
    	}
    	return megethos;
    }

  2. #2
    Registered User
    Join Date
    Oct 2001
    Posts
    2,934
    >I have a warning into the main that A hasn't been initialized
    This is correct. A new address is given to A in function FillStruct, but since C passes arguments by value, this new address is never seen once the function returns to main(). Try this instead.
    Code:
    #include<stdio.h>
    #include<time.h>
    #include<stdlib.h>
    
    int FillStruct(int **A);
    
    int main(void){
    	
    	int megethos,*A,epilogi;
    	srand(time(NULL));
    	
    	do{
    		printf("--------------------------\n       Main Menu\n--------------------------\n");
    		printf("Give a choice: ");
    		scanf("&#37;d",&epilogi);
    		switch (epilogi) {
    		case 1:
    			megethos=FillStruct(&A);
    			break;
    	.
    	.
    	.
    	.
    	.
            }
    	return 0;
    }
    
    int FillStruct(int **A)
    {
    	int type,zevgaria,thesi,temp,i,megethos;
    	printf("Please give the length of the struct:");
    	scanf("%d",&megethos);
    
    	*A = calloc(megethos,sizeof(**A));
    	if (*A==NULL){
    		printf("ALLOCATING MEMMORY ERROR");
    		exit(1);
    	}
    	return megethos;
    }

  3. #3
    Registered User
    Join Date
    Jun 2007
    Posts
    11
    Thanks, you are right! And if i want to refer to the array in that function, i have to write *A[]??
    For example why something like that is wrong??
    Code:
    int FillStruct(int **A)
    {
    	int type,zevgaria,thesi,temp,i,megethos;
    	printf("Please give the length of the struct:");
    	scanf("%d",&megethos);
    
    	*A = calloc(megethos,sizeof(**A));
    	if (*A==NULL){
    		printf("ALLOCATING MEMMORY ERROR");
    		exit(1);
    	}
            for(i=0;i<megethos;i++) *A[i]=i ;
    	return megethos;
    }
    I don't have any errors but it can't be executed either

  4. #4
    Registered User
    Join Date
    Oct 2001
    Posts
    2,934
    >And if i want to refer to the array in that function, i have to write *A[]??
    Almost. You need (*A)[]:
    Code:
            for(i=0;i<megethos;i++) (*A)[i]=i ;

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Dynamic Array Resizing
    By dld333 in forum C++ Programming
    Replies: 13
    Last Post: 11-03-2005, 11:13 PM
  2. need help with dynamic array syntax
    By soldyne in forum C Programming
    Replies: 3
    Last Post: 10-11-2005, 01:59 PM
  3. Class Template Trouble
    By pliang in forum C++ Programming
    Replies: 4
    Last Post: 04-21-2005, 04:15 AM
  4. 2D dynamic array problem
    By scsullivan in forum C Programming
    Replies: 3
    Last Post: 12-30-2002, 09:02 PM
  5. Dynamic array allocation and reallocation
    By purple in forum C Programming
    Replies: 13
    Last Post: 08-01-2002, 11:48 AM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21