Array of structs

This is a discussion on Array of structs within the C Programming forums, part of the General Programming Boards category; is this possible ?? Code: struct s{ char *name; }MyArray[5]; is this will create array of structs or i am ...

  1. #1
    C 1337 Meshal's Avatar
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    Array of structs

    is this possible ??

    Code:
    struct s{
    char *name;
    }MyArray[5];
    is this will create array of structs or i am wrong because after compiling it i get the same answer ..

    exampl when i put to the first element "first_name"
    and the second element "second_name"
    and if i output the first elemenet .. it will contain "second_name"..
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  2. #2
    C 1337 Meshal's Avatar
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    this is More advance exmaple :

    Code:
    #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    
    #define MAX2 100
    
    struct s 
    {
    	char* id;              //array of structures Maximum of Five students,
    };
    
    int main(int argc,char *argv[])
    {
    
    	struct s MyArray[5];
    	FILE *fp;
    
    	char *r = NULL;
    	char d[2];
    
    	int n,j,k,m,l;
    	int i=0;// counters
    	int u=0;
                     
    	
    	char line[MAX2];
    
    
    	if ((fp = fopen(argv[1],"r")) == NULL){
    	    printf("cannot open the file that you specified\nThe file has to be in the same directory\n");
    	    exit(1);}   
                    d[0] = ':';
                    d[1] = '\0';              
    	
    	i = 0;
    	while((fgets(line,100,fp)) != NULL  )
    	{
    		n=0;
    		for(k = 0; k < 100; k++){
    			if (line[k] == '\n'){
    				line[k] = '\0';
    				break;
    			}
    
    		}
    
    		r = strtok(line,d);
    		MyArray[i].id = r;
    		n = strlen(r);
    		MyArray[i].id[n] = '\0';
    
    		++i;
    		
    	}
    
    	printf("%s\n",MyArray[0].id);
    	
    	fclose(fp);
    	return 0;
    }

    the file-input

    Code:
    s1:csc212,csc281,csc361
    s2:csc361,csc336,csc329
    s3:csc336,csc327,csc212,csc281
    s4:csc342,csc327,csc311,csc305
    s5:csc212,csc281,csc327,csc380
    output of the program:

    Code:
    s5
    why every element in the array print s5 , i think it should print s1 ???
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  3. #3
    and the hat of int overfl Salem's Avatar
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    Well you have a pointer, so everything ends up pointing at the same thing.

    So have something like
    char id[20];

    And
    strcpy( MyArray[i].id, r );


    > n = strlen(r);
    > MyArray[i].id[n] = '\0';
    These two lines are a waste of time. strtok() writes a \0, and strlen() returns the index position of the \0 (otherwise known as the length).
    So all you're doing is overwriting one \0 with another \0.


    > for(k = 0; k < 100; k++)
    See the FAQ, there are easier ways of removing the \n.
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  4. #4
    C 1337 Meshal's Avatar
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    thanks Salem , and is there a way to do it dynamicly ??
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  5. #5
    Fear the Reaper...
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    Code:
    struct s* MyArray = malloc(num*sizeof(struct s))
    Will give you num stucts.
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  6. #6
    Fear the Reaper...
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    ummm...no. id is a char*, so if you wanted to do that, you'd want to allocate chars instead of struct s's.
    Last edited by Happy_Reaper; 05-05-2007 at 05:14 PM. Reason: EDIT : Meshal, why'd you delete your post ?
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  7. #7
    C 1337 Meshal's Avatar
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    and if i have a struct that contain multiple id`s .. like this :

    Code:
    struct s{
    char *id[4] ;
    }MyArray[5];
    can i do what salem say`s .. or it will be a problem

    i mean is this true :

    Code:
    MyArray[i].d[j] = malloc(sizeof(char*));
    strcpy(MyArray[i].id[j],r);

    so what is the solution to this problem !!
    Last edited by Meshal; 05-05-2007 at 07:16 PM.
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  8. #8
    C 1337 Meshal's Avatar
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    thanks guys , finally i got every things works Ok .. "thanks word" is not enough to thank you..

    and i appreciate your help all of you .

    sorry my english is bad ,
    Last edited by Meshal; 05-05-2007 at 08:53 PM.
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  9. #9
    and the hat of int overfl Salem's Avatar
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    > MyArray[i].d[j] = malloc(sizeof(char*));
    > strcpy(MyArray[i].id[j],r);
    It should be
    Code:
    if ( (MyArray[i].d[j] = malloc( strlen(r) + 1 )) != NULL ) {
        strcpy(MyArray[i].id[j],r);
    } else {
        // out of memory
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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