Thread: Help with file read/write

Hi, i'm learning basic file read/write methods and i'm having trouble with this simple program.
It compiles without error but the text file does not show up on my desktop.
I've tried replacing "~" with "file://" and i am still not getting any results
I'm using gcc in Terminal(Mac)

Code:

#include <stdio.h>

int main() {
	FILE *handle;
	handle = fopen("~/Users/Jem/Desktop/test.txt","w");
	
	if (handle==NULL) {
		printf("Error opening file\n");
	}else {
		fprintf(handle,"TESTING");
		fclose(handle);
	}
	return 0;
}

Or even better, recognize what ~ means: ~ means your own personal home directory. So perhaps you want "~/Desktop/test.txt" instead.

thanks!
Also. how can i read the contents of the file? I tried the code below but i got this error:
"c:10: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘struct FILE *’ "
so i tried casting with "(char*)" in front of "handle" in the printf(); that time it compiled but nothing was printed. Help appreciated.

Code:

#include <stdio.h>

int main() {
	FILE *handle;
	handle = fopen("/Users/Jem/Desktop/test.txt","r");
	
	if (handle==NULL) {
		printf("Error opening file\n");
	}else {
		printf("%s",handle);
		fclose(handle);
	}
	return 0;
}

I do not believe fopen will automatically expand the ~ variable into your home directory.

EDIT: Beaten!

handle is a FILE pointer, not a string you can print. Read the FAQ and the C File I/O tutorial.

Originally Posted by Dino

~ is understood in the shell, but not in fopen.

Oh well spotted. Sorry.

ok, i used fscanf() instead and got some unexpected results. The test.txt file says "TESTING... TESTING"
when i run the program, i get the output:

Code:

TESTING?

here's the whole thing:

Code:

#include <stdio.h>

int main() {
	char message[50];
	FILE *handle;
	handle = fopen("/Users/Jem/Desktop/test.txt","r");
	
	if (handle==NULL) {
		printf("Error opening file\n");
	}else {
		fscanf(handle,"%s",message);
		fclose(handle);
		printf("%s\n",message);
	}
	return 0;
}

Originally Posted by bluej322

ok, i used fscanf() instead and got some unexpected results. The test.txt file says "TESTING... TESTING"
when i run the program, i get the output:

Code:

TESTING?

here's the whole thing:

Code:

#include <stdio.h>

int main() {
	char message[50];
	FILE *handle;
	handle = fopen("/Users/Jem/Desktop/test.txt","r");
	
	if (handle==NULL) {
		printf("Error opening file\n");
	}else {
		fscanf(handle,"%s",message);
		fclose(handle);
		printf("%s\n",message);
	}
	return 0;
}

1) %s will not read past a space. If you want to read a line which may include spaces, then fscanf is not for you. Look at fgets.

2) Did you type three actual periods, or do you have one of them fancy symbols in your file?

Originally Posted by tabstop

1) %s will not read past a space. If you want to read a line which may include spaces, then fscanf is not for you. Look at fgets.

2) Did you type three actual periods, or do you have one of them fancy symbols in your file?

Thanks. I typed three periods

Originally Posted by bluej322

Thanks. I typed three periods

Yeah, okay, I walked into that. Did your editor turn them into a funny symbol for you? (Some editors do.) Open up a terminal and type "cd ~/Desktop" and then "cat test.txt" and see what you see. If you have three separate symbols in your file, then you should have seen three separate symbols in your output.

Originally Posted by tabstop

Yeah, okay, I walked into that. Did your editor turn them into a funny symbol for you? (Some editors do.) Open up a terminal and type "cd ~/Desktop" and then "cat test.txt" and see what you see. If you have three separate symbols in your file, then you should have seen three separate symbols in your output.

Ok, it printed:

TESTING? TESTING

Originally Posted by bluej322

Ok, it printed:

TESTING? TESTING

So that means that you no longer have three dots in your program, but one funny character. Easiest thing to do is probably remember what editor you were using when you made that text file, and then never use it again.

Originally Posted by tabstop

So that means that you no longer have three dots in your program, but one funny character. Easiest thing to do is probably remember what editor you were using when you made that text file, and then never use it again.

I'm using TextEdit, and i made sure it's plain text(instead of the default rich text format).

Here's another question, how can i read the contents of an entire file? Do i have to go through line by line using fgets()?