Thread: Help with reading a file

if I have a file, marks.dat:
8
5 9 3 7 8 7 8 9

How to I read the first line(8) and put it into num_marks, and put the rest of the numbers into an array (marks[])?

1. Read the first number and call it num_marks.
2. For i = 0 to (num_marks-1): Read in a number and call it marks[i].

Notice that you won't be able to use num_marks as an array size in the declaration of marks[], so you'll need to either pick a "large enough" number or use malloc().

I still don't completely understand what to do. I'm kinda new with this stuff, so if you could be a bit more specific that would help, thanks.

Files

Loops

Code:

//---------------------------------------------------------------------------

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define One 1
#pragma hdrstop

//---------------------------------------------------------------------------

/* Read some data from a binary file into an array. */

void FillArrayFromBinaryFile(const char *filename, int **ptrArray, int *ArraySz)
{
	if(!filename)
	{
		fprintf(stderr, "NULL input filename.\n");
		return;
	}
	else
	{
		FILE *filePtr = NULL;
		if((filePtr = fopen(filename, "rb")) == NULL)
		{
			fprintf(stderr, "Error Opening:\"%s\" file.", filename);
			return;
		}
		else
		{
		unsigned int Index = 0;
		int *nArray = calloc(One, sizeof(int));
		if(!nArray)
		{
			fprintf(stderr, "Memory Error.\n");
			fclose(filePtr);
			return;
		}
			for(;;)
			{
			   if(1 != fread(&nArray[Index], sizeof(int), 1, filePtr))
				break;
			   /* Each time. */
			   Index++;
			   nArray = realloc(nArray, Index+1 * sizeof(int));
			   fseek(filePtr, Index * (sizeof(int)+sizeof(char)), SEEK_SET);
			}
			*ptrArray = nArray;
			*ArraySz = Index;
			fclose(filePtr);
			return;
		}
	}
}
void PrintArray(int *nArray, int Sz)
{
	static int Index = 0;
	for(Index = 0; Index < Sz; Index++)
		printf("%d ", nArray[Index]);
	printf("\n");
}
void WriteArrayToBinaryFile(const  char *filename, int *nArray, int nSz)
{
	if(!filename)
		return;
	else
	{
		FILE *filePtr = NULL;
		if((filePtr = fopen(filename, "wb")) == NULL)
		{
			fprintf(stderr, "Error Opening:\"%s\" file.", filename);
			return;
		}
		{
			int Index  = 0;
			char cChar = ' ';
			for(Index = 0; Index < nSz; Index++)
			{
				fwrite(&nArray[Index], sizeof(int), 1, filePtr);
				fwrite(&cChar, sizeof(char), 1, filePtr);
			}
			fclose(filePtr);
			return;
        }
    }
}

#pragma argsused
int main(int argc, char* argv[])
{
	int nArraySz = 0;
	int nArray[4];
	int *ptrToArray = NULL;
	nArray[0] = 1;
	nArray[1] = 4;
	nArray[2] = 6;
	nArray[3] = 12;
	WriteArrayToBinaryFile("Array.dat", nArray, 4);
	memset(nArray,0, sizeof(nArray));
	FillArrayFromBinaryFile("Array.dat", &ptrToArray, &nArraySz);
	PrintArray(ptrToArray, nArraySz);
	free(ptrToArray); ptrToArray = NULL;
	printf("Hit enter to continue...\n");
	getchar();
	return 0;
}
//---------------------------------------------------------------------------

The above code will not solve your problem, but will give you a point to start. It writes an array to a binary file, then sets the array elements to zero and try to read them back again from the binary file. The difference is that using realloc i dont care what is the sizeof the array(number 8) in the binary file.

I just write to the file:

1 4 6 12

and try to get them back again.

*Possible bugs included. *

Bokarinho.