Thread: Example needed

Hi, could anyone provide a small working example on how to write and read binary files. Let say i have 3 arrays , a char *array , int *array1 and unsigned int *array2. How would i store this on disc in binary format and then read it from the disc (i need all 3 arrays to be in a single binary on disc , is this possible ?)


thank you very much,

baxy

Originally Posted by baxy

Hi, could anyone provide a small working example on how to write and read binary files. Let say i have 3 arrays , a char *array , int *array1 and unsigned int *array2. How would i store this on disc in binary format and then read it from the disc (i need all 3 arrays to be in a single binary on disc , is this possible ?)


thank you very much,

baxy

It sounds like you want to use a struct, which takes disparate datatypes that relate to one object, and puts them together into a single object. Think of a student with an ID, a major, an age, a year in school, and several classes and a GPA. They can all go into one struct, and you can make an array of those structs if you like.

So you'd wind up with just one file of structs - and there are zillions of examples of writing out binary files. Google one of them.

If you get stuck, come back and post up your code, and tell us what you're stuck on. We're here to help, but want to see some starting effort - which is forum policy.

The declarations: char *array, int *array1, and unsigned int *array2 do not specify arrays. They specify pointers.

arrays are not pointers and pointers are not arrays. I suggest you read comp.lang.c.FAQ. particularly section 6.

hi, ok here is my attempt but i don't deg why is it not working. so i took Adak's advice and it is writing sonething but i cannot read it ????

write.c

Code:

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


struct data	{
		int *count;
		long *Info;

}data;

int main(){
		FILE *fileOut;
		struct data *myData = emalloc(sizeof(*myData));
		myData->count = (int *) emalloc(sizeof(int) * 100);
		myData->Info = (long *) emalloc(sizeof(long) * 100);
		int i = 0;
		for (i=0;i<100;i++){
			myData->count[i] = i+i;
			myData->Info[i] = i*i;
		}

		fileOut=fopen("test.bin","wb");
		if (!fileOut)
		{
			printf("Unable to open file!");
			return 1;
		}
		fwrite(&myData, sizeof(struct data), 1, fileOut);

		fclose(fileOut);
		
		return 0;
}

read.c

Code:

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

	/* Our structure */
struct data	{
		int *count;
		long *Info;

}data;


int main(){
		FILE *fileIn;
		struct data *myData = emalloc(sizeof(*myData));
        int i;
        myData->count = (int *) emalloc(sizeof(int) * 100);
		myData->Info = (long *) emalloc(sizeof(long) * 100);
		fileIn=fopen("test.bin","rb");
		if (!fileIn)
		{
			printf("Unable to open file!");
			return 1;
		}
        printf("ggg\n");
		fread(&myData,sizeof(struct data),1,fileIn);
		        printf("ggg\n");
	    for (i=0;i<100;i++){
	      printf("%d..%ld\n",myData->count[i],myData->Info[i] );
	    }

		fclose(fileIn);
		return 0;
	}

so it is writing but when it comes to reading i get: Segmentation fault (core dumped)

Thnx everything is working, i learned something new today

Hi

well more problems. So now i want to increase the reading and writing buffer. I don't want it to write one byte at the time or read one byte at the time. so i did this when writting:

Code:

FILE *fileOut;
fileOut=fopen("test.bin","wb");
int tmp[100];
int i;

  if (!fileOut){
	printf("Unable to open file!");
  }
  
  for(i=0;i<10000;i++){
    
    if (i%100 == 0){
      fwrite(&tmp, sizeof(Int64), 100, fileOut);
    }
    tmp[i%100] = i;
      
  }

  fclose(fileOut);

but when i read it i get all the zerros

??

THANK YOU ; it is working now