help with reading contents from file in C

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hey guys,

if you saw my last question, i asked about reading information from files. so far, i have been doing a lot of research and have got something, but it doesn't exactly work too well.

i have a text file called file.txt with a simple letter 'l'. And this is my code for trying to read it:

C++

#include <stdio.h>

int main(int argc, const char **argv[])
{
	FILE *f = fopen("file.txt", "r");
	fseek(f, 0, SEEK_END);
	long pos = ftell(f);
	fseek(f, 0, SEEK_SET);
	
	char bytes[pos];
	fread(bytes, sizeof(char), 1, f);
	fclose(f);
	
	int i = 0;
	for (i = 0; i <= sizeof(bytes); i++)
	{
		printf("%d - %c", bytes[i], bytes[i]);
		printf("\n");
	}
	getchar();
}

what it does is it prints out '108 - l' which is what I want. And then on the next line, it prints out '41 - >'. And then when I try to add more characters to the text file, it just does some more random stuff again. Can someone please tell me what I'm doing wrong and edit my code to show me what I need to do?

thanks a heap,
Fletcher

Posted 8-Oct-13 0:06am

Member 8378691

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CPallini · Answer 1 · 2013-10-08T00:12:00

Solution 1

Quote:
fread(bytes, sizeof(char), 1, f);

Change to

C

fread(bytes, sizeof(char), pos, f);

(You should also check its return value)

[update]
As pasztorpisti correctly pointed out, you cannot declare a C array that way. You either

allocate dynamically the array (using malloc function)

Or

Use a very big static array (and make sure your program doesn't overrun it)

[/update]

Posted 8-Oct-13 0:12am

CPallini

Updated 8-Oct-13 0:49am

v2

Comments

Member 8378691 8-Oct-13 6:26am

how do I check the return value?

CPallini 8-Oct-13 6:50am

fread returns the number of items read. Its return value should be equal to pos.

pasztorpisti 8-Oct-13 6:59am

+5 for the tips - I was lazy to write them :-)

CPallini 8-Oct-13 7:02am

Thanks (your lazyness :-) ).

pasztorpisti · Answer 2 · 2013-10-08T00:13:00

Solution 2

C++

char bytes[pos];
fread(bytes, sizeof(char), 1, f);

The size of a C style array must be compile time constant and before closing the file you read in just one byte.

Posted 8-Oct-13 0:13am

pasztorpisti

Comments

CPallini 8-Oct-13 6:43am

Ouch, I missed that! My 5.

Richard MacCutchan · Answer 3 · 2013-10-08T01:09:00

Solution 3

See the MSDN documentation[^] for fread. Also a Google search will find some tutorials that will help you.

Posted 8-Oct-13 1:09am

Richard MacCutchan

Member 8378691 · Answer 4 · 2013-10-13T19:58:00

Solution 4

hey guys,

thanks to some help from you and another one of my friends, i finally got some code that works, here it is:

C++

int main(int argc, const char *argv[])
{
	int x;
	int xpos = 0;
	FILE *bin = fopen((const char*)argv[1], "r");
	int length = ftell(bin);
	program = (int*) malloc(length);
	while ((x = (int)getw(bin)) != EOF)
	{
		program[xpos] = x;
		xpos++;
	}
	
	run();
	return 0;
}

Posted 13-Oct-13 19:58pm

Member 8378691

Comments

Richard MacCutchan 14-Oct-13 3:09am

That should not even compile let alone run, and even then the results you get are unlikely to be what you want.