Help with file read/write

This is a discussion on Help with file read/write within the C Programming forums, part of the General Programming Boards category; Hi, i'm learning basic file read/write methods and i'm having trouble with this simple program. It compiles without error but ...

  1. #1
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    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;
    }

  2. #2
    Jack of many languages Dino's Avatar
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    Lose the tilde.
    Mac and Windows cross platform programmer. Ruby lover.

    Quote of the Day
    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

  3. #3
    and the Hat of Guessing tabstop's Avatar
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    Or even better, recognize what ~ means: ~ means your own personal home directory. So perhaps you want "~/Desktop/test.txt" instead.

  4. #4
    Jack of many languages Dino's Avatar
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    ~ is understood in the shell, but not in fopen.
    Mac and Windows cross platform programmer. Ruby lover.

    Quote of the Day
    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

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    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;
    }

  6. #6
    a_capitalist_story
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    I do not believe fopen will automatically expand the ~ variable into your home directory.

    EDIT: Beaten!

  7. #7
    a_capitalist_story
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    handle is a FILE pointer, not a string you can print. Read the FAQ and the C File I/O tutorial.

  8. #8
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Dino View Post
    ~ is understood in the shell, but not in fopen.
    Oh well spotted. Sorry.

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    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;
    }

  10. #10
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by bluej322 View Post
    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?

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    Quote Originally Posted by tabstop View Post
    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

  12. #12
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by bluej322 View Post
    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.

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    Quote Originally Posted by tabstop View Post
    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

  14. #14
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by bluej322 View Post
    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.

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    Quote Originally Posted by tabstop View Post
    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()?

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