Thread: File reading and writing

I tried to make a program that takes a file and turns it into a bunch of smaller files, but the output files are always empty... can someone tell me where I'm messing up?

Code:

#include "windows.h"
#include "stdio.h"
#include "string.h"

void main(){
	FILE *fl1, *fl2;
	char Fn[255], On[255], end=0;
	void *goan;
	int Num, Siz, l1, l2, oh, oh2;

	printf("Name of file to open: ");
	scanf("%s",&Fn);
	printf("\nBase name of output files : ");
	scanf("%s",&On);
	printf("\nNumber of files to make (less than 1,000): ");
	scanf("%d",&Num);
	printf("\nSize of files : ");
	scanf("%d",&Siz);
	printf("\n\nWorking: ");
	fl1=fopen(Fn,"r");
	for(l1=0;l1<Num;l1++){
		On[0]=(char)(48+(int)(l1/100));
		On[1]=(char)(48+(int)((l1-100*((int)On[0]-48))/10));
		On[2]=(char)(48+(l1-100*((int)On[0]-48)-10*((int)On[1]-48)));
		fl2=fopen(On,"w");
		goan=malloc((0x1000*Siz));
		if(goan==NULL){
			printf("\n\n\tFAILURE\n");
			fclose(fl1);
			fclose(fl2);
			scanf("%c",end);
			scanf("%c",end);
			return;
		}
		oh=fread(goan,1,(0x1000*Siz),fl1);
		printf("\noh= %d",oh);
		oh2=fwrite(goan,1,oh,fl2);
		if((0x1000*Siz)!=oh2){
			printf("\nLooks like an error, but I could be wrong...");
		}
		fclose(fl1);
		free(goan);
	}
	fclose(fl1);
	printf("\n\n\tDone\n");
	scanf("%c",end);
	scanf("%c",end);
}

The first file is really small, around 100 bytes, and all the rest are 0 bytes.

Code:

#include "windows.h"
#include "stdio.h"
#include "string.h"

void main(){
	FILE *fl1, *fl2;
	char Fn[255], On[251], end=0;
	void *goan;
	int Num, Siz, l1, l2, oh, oh2;

	printf("Name of file to open: ");
	scanf("%s",Fn);
	printf("\nBase name of output files : ");
	scanf("%s",On);
	printf("\nNumber of files to make (less than 1,000): ");
	scanf("%d",&Num);
	printf("\nSize of files (KBs): ");
	scanf("%d",&Siz);
	printf("\n\nWorking: ");
	fl1=fopen(Fn,"r");
	if(fl1==NULL){
		printf("\n\n\tFAILURE- file1\n");
		fclose(fl1);
		scanf("%c",end);
		scanf("%c",end);
		return;
	}
	for(l1=0;l1<Num;l1++){
		sprintf(Fn, "%03d_", l1);
		memcpy(&Fn[4],On,251*sizeof(char));
		fl2=fopen(Fn,"w");
		if(fl2==NULL){
			printf("\n\n\tFAILURE- file2\n");
			fclose(fl1);
			fclose(fl2);
			scanf("%c",end);
			scanf("%c",end);
			return;
		}
		goan=malloc((0x400*Siz));
		if(goan==NULL){
			printf("\n\n\tFAILURE- malloc\n");
			fclose(fl1);
			fclose(fl2);
			scanf("%c",end);
			scanf("%c",end);
			return;
		}
		oh=fread(goan,1,(0x400*Siz),fl1);
		printf("\noh= %d",oh);
		oh2=fwrite(goan,1,oh,fl2);
		if((0x400*Siz)!=oh2){
			printf("\nLooks like an error...");//prints every time
		}
		fclose(fl2);
		free(goan);
	}
	fclose(fl1);
	printf("\n\n\tDone\n");
	scanf("%c",end);
	scanf("%c",end);
}

1. You're missing a header file
2. A lot of your printf or scanf calls are using mis-matched conversion strings and parameters.

Code:

$ gcc -W -Wall -ansi -pedantic -O2 foo.c
foo.c:5: warning: return type of 'main' is not `int'
foo.c: In function `main':
foo.c:24: warning: format argument is not a pointer (arg 2)
foo.c:25: warning: format argument is not a pointer (arg 2)
foo.c:36: warning: format argument is not a pointer (arg 2)
foo.c:37: warning: format argument is not a pointer (arg 2)
foo.c:40: warning: implicit declaration of function `malloc'
foo.c:45: warning: format argument is not a pointer (arg 2)
foo.c:46: warning: format argument is not a pointer (arg 2)
foo.c:56: warning: implicit declaration of function `free'
foo.c:60: warning: format argument is not a pointer (arg 2)
foo.c:61: warning: format argument is not a pointer (arg 2)
foo.c:9: warning: unused variable `l2'

> printf("\nLooks like an error...");
This will always happen at some point, unless your file just happens to be the exact same size as the value you input.

> fl1=fopen(Fn,"r");
You should use "rb" and "wb" if you intend on using fread/fwrite

> goan=malloc((0x400*Siz));
There is no point in calling this (and free) inside the loop.
Just allocate it once outside the loop before you start, then free it again when you leave the loop.

I don't know what you meant about me missing a header file, or calling mis-matched conversion strings, but I took your other 3 pieces of advice, and changing "r" and "w" to "rb" and "wb" made it work. Thanks.

> scanf("%c",end);
Writes a character where you don't expect - could be anywhere in memory
That's what the warnings all mean.

scanf("%c",&end);
All scanf parameters need to be pointers of one sort or another.

Oh yea, oops. hehe...