need help about array of struct

Hi all, i need to understand how to solve the following exercise, I have a structure:

Code:

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#define FRAMESIZE 17                // carframe size

typedef struct {
        char *name;        // owner name
        char *surname;  // owner surname
        char carframe[FRAMESIZE];    // carframe number(alphanumeric)
        struct {
                int d;                // day
                int m;                // month
                int y;                // year
        } matr;                                                // matriculation date
} Vehicle;

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I have to implement a function Vehicle *buildarchive(char *text, int *n) that creates a dynamically allocated array of struct Vehicle whose values are contained into the string text and that returns in *p the number of struct, each string is divided by rows in order to contain datas of each vehicle, every row has the following format: N;S;F;D;M;Y where N is the owner's name, S the surname etc.. and terminates with the character '\n', so if the text is:

Code:

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Mario;Dell'Olio;ABCD1234567899GHT;12;1;2004
Laura;Di Carlo;ABBB0987654321HGT;3;10;1999
Maria Luisa;Crociani Sforza Pallavicini;NNNN1234567890BFB;25;11;2006       
Giorgio;Verdoni;AAAA09876FFT54321;10;10;2009

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the function creates the following array, and return in *p the value 4:

Code:

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[0] = {"Mario", "Dell'Olio", ABCD1234567890GHT, {12, 1, 2004}}
[1] = {"Laura", "Di Carlo", ABBB0987654321HGT, {3,10,1999}}
etc till [3] = ...

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now what i did till now is basically just printing on screen each row:

Code:

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#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define FRAMESIZE 17                // carframe size

typedef struct {
        char *name;
        char *surname;
        char carframe[FRAMESIZE];
        struct {
                int d;                // day
                int m;                // month
                int y;                // year
        } matr;                                                // matriculation date
} Vehicle;

Vehicle *buildarchive(char *text, int *n);
int main()
{
        char string[] = {"Mario;Dell'Olio;ABCD1234567899GHT;12;1;2004\n"
                                                "Laura;Di Carlo;ABBB0987654321HGT;3;10;1999\n"
                                                "Maria Luisa;Crociani Sforza Pallavicini;NNNN1234567890BFB;25;11;2006\n"                       
                                                "Giorgio;Verdoni;AAAA09876FFT54321;10;10;2009\n"
                                                };

        int *p;
       
        buildarchive(string, p);

        return 0;       
}
Vehicle *buildarchive(char *text, int *n)
{
        int count = 0, i;
        char *text_temp;
        char *text_tmp;
        text_temp = text;
        text_tmp = text;
       
        /* counts rows */
        while(*text_tmp != '\0') {
                if(*text_tmp == '\n') {
                        count++;
                }
                *text_tmp++;
        }
       
        Vehicle *array = (Vehicle*)malloc(count * sizeof(Vehicle));
       
        while(*text != '\0') {                          // iterates till the string reaches the '\0' character
                while((*text_temp != ';')&&(*text_temp != '\n')) {               
                        printf("%c", *text_temp);
                        *text_temp++;                       
                }                       
                text = text_temp;               
                if(*text == '\n') {
                        printf("\n");
                }
                *text++;
                text_temp = text;
        }
        printf("\nsentences = %d (counter)\n", count);
}

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the counter counts the number of rows so that i could create an array of Vehicle but im stuck trying to understand how to put each information into this array, any suggestion? thanks ^^

Well, you would access the individual elements and members like this:

Code:

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array[0].matr.d = 31;

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Obviously, the "name" member will need to be malloc'd memory before use.

BTW, you do not need to typecast void* in C:

Code:

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Vehicle *array = (Vehicle*)malloc(count * sizeof(Vehicle));

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This is fine:

Vehicle *array = malloc(count * sizeof(Vehicle));

I still have a problem.. now i'm trying to save each string so that i will be able to put them into the array, but i got an error with realloc: invalid next size error

Code:

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char *text_temp;
        char *text_tmp;
        char *hold;
        text_tmp = text_archive;  // text is the original string
        text_temp = text_archive;
       
        char *s1 = malloc(50*sizeof(char));
        char *ptr = malloc(25*sizeof(char));
        int offset = 0;
       
        while(*text_tmp != '\n') {
                hold = text_temp;
                while(*text_temp != ';') {
                        offset++;
                        *text_temp++;
                }
                ptr = strncpy(s1, hold, offset);    // strncpy saves each string
                printf("%s\n", ptr);
                ptr = realloc(ptr, offset+1);
                offset = 0;
                *text_temp++;
                *text_tmp++;
        }
}

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it does the first 3 iterations and than shows the error, i want to keep each substring of the string text_archive, each one separated by the ';' character.. i must have done something wrong with realloc() but realloc(ptr, offset+1) seems fine to me..any suggestion on why i get the error?

I think it should be :

Code:

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ptr = realloc(ptr, (offset+1) * sizeof(*ptr));

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Haven't tested it though.

http://cboard.cprogramming.com/c-pro...malloc-ed.html

If realloc fails, you will lose whatever ptr contains. Consider storing the return value elsewhere first and checking for validity before assigning it to ptr.


Quzah.

I solved my problem, the function creates the array well and everything works fine but I still dont understand how to return a pointer to the number of structures used, the function Vehicle *buildarchive(char *text, int *n) should return n which in my case is 4 because the number of structures is equal to the number of rows of the string, so i made n = &count, which is the number of rows, but if I return that value i got random numbers, any ideas?

if I do a print of n inside the function it shows that its value is right, however i still cant understand how to return its value since the function should return a pointer to Vehicle.. :(

Quote:

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Originally Posted by rob90

I solved my problem, the function creates the array well and everything works fine but I still dont understand how to return a pointer to the number of structures used, the function Vehicle *buildarchive(char *text, int *n) should return n which in my case is 4 because the number of structures is equal to the number of rows of the string, so i made n = &count, which is the number of rows, but if I return that value i got random numbers, any ideas?

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No need to return n if you have passed a pointer to count in buildarchive().
Putting it indirectly, n is a pointer to count while *n is the same as count.

Quote:

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Originally Posted by rob90

if I do a print of n inside the function it shows that its value is right, however i still cant understand how to return its value since the function should return a pointer to Vehicle.. :(

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Are you printing n or *n? Since n is the location of count while *n is count.
Returning from buildarchive(), count in the calling function will be equal to *n.

I'm printing *n, its value is right, but i dont need to print it inside the function, i need to return it, however this function Vehicle *buildarchive(char *text, int *n) should return a pointer to Vehicle while *n is a pointer to int, that's what i don't understand..

Quote:

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Originally Posted by rob90

I'm printing *n, its value is right, but i dont need to print it inside the function, i need to return it, however this function Vehicle *buildarchive(char *text, int *n) should return a pointer to Vehicle while *n is a pointer to int, that's what i don't understand..

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Function Vehicle *buildarchive(char *text, int *n) explicitly returns Vehicle *, and implicitly returns *n.
You are not explicitly returning *n, but count in the calling function acquires that value rather indirectly.