need help about array of struct

[rob90]

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

#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;

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:

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

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

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

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

#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);
}

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 ^^

[MK27]

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

array[0].matr.d = 31;

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

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

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

This is fine:

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

[rob90]

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

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++;
	}
}

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?

[zalezog]

I think it should be :

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

Haven't tested it though.

[quzah]

How Do You Add Onto Dynamic Memory After You've Already Malloc-ed It?

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.

[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?

[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..

[itCbitC]

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?

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.

[itCbitC]

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..

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.

[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..

[itCbitC]

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..

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.