Simple text file editor - Having some problems - C program

This is a discussion on Simple text file editor - Having some problems - C program within the C Programming forums, part of the General Programming Boards category; Hi there, I'm having some problems with my latest programming attempt. ---------------------------------------------------------------------------------------------------------------- So you know what I'm talking about, the ...

  1. #1
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    Question Simple text file editor - Having some problems - C program

    Hi there,

    I'm having some problems with my latest programming attempt.

    ----------------------------------------------------------------------------------------------------------------
    So you know what I'm talking about, the question is:
    "Write a simple editor.

    The editor should first ask the user for the name of a file to edit.
    You may assume that the file already exists.

    Files will be restricted to exactly 23 lines of text, with no line longer than 70 characters.

    The editor should display the text in the file starting at the top of the screen.

    The 24'th line is used by the user to give commands to the editor. The prompt should be Command:

    The only commands that are available are:

    D number which will delete the line with that number. All lines after that one will move up one.
    The new 23rd line at the bottom will be empty.

    I number Will insert the text typed on the 25'th line before the line with that number
    All lines will move down one to accommodate the new line.
    The old 23'rd line will be discarded.

    R number Will replace, with the text typed on the 25'th line, the line with that number

    S Will save away the changes, by writing the text back to disk.

    Q Will quit the program

    eg

    Command: I 6
    this new line will be placed between line 5 and line 6 of the file

    After each command the screen should be cleared using the clrscr() function (in <conio.h>).
    The text should then be displayed again.

    Line numbers given by the user will, in true computer science style, start from 0 and go to 22.
    "
    ---------------------------------------------------------------------------------------------------------------


    The code I have written is as follows:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <conio.h>
    #include <string.h> 
    
    char text[23][80];
    
    int main() {
    	int i, num; 
    	char c[80];
    	char temp[80];
    	FILE *g;
    	
    	printf("Enter file name:\n");
    	gets(c);  
    	g = fopen(c, "r"); 
    	
    	if(g == NULL) {
    		printf("Error: File did not open");
    		exit(0);
    	}
    	while(fgets (text[i], 80, g) !=NULL) {   
    		i++;
    		/* started getting the microsoft send/dontsend error here */
    	}
    	fclose(g);
    	system("cls");  
    	
    	for(i=0; i<23; i++) {
    		printf("%s", text[i]);
    	}
    	printf("Command:");
    	sscanf(temp, "%c %d", &c, &num); 
    	
    	while(temp != "Q") { 
    		if(temp == "R") {
    			fgets(text[num],80,stdin);
    		}
    		if(temp == "D") {
    			for(i=21; i<num; i++) {  /*"loop from num to 21"...should it be a while loop?? */
    				strcpy(text[i], text[i+1]);
    				/* "\n" (line 22) ??? */ 
    			}
    		}
    		if(temp == "I") {
    			for(i=22; i>num; i--) {
    				strcpy(text[i], text[i-1]);
    			}
    		}
    		if(temp == "S") {
    			for(i=0; i<23; i++) {
    				fprintf(g, text[i]);
    			}
    		}	
    	} 	     		
    }

    When I run the program in my GCC compiler, the program runs. Then it prompts me "Enter file name" (so far so good) Then when I enter in my file name (the one I am using is a text file called junk.txt - basicly a list of movies numbered 0 to 22) it comes up with the microsoft "send/don't send" error. then crashes. The program runs further if I delete everything in my junk.txt file... ie a blank txt file. If I do this, it will prompt me to enter a "Command:".

    When I debug my program, it stops me at this line, so I'm thinking, this might be the problem:
    Code:
    while(fgets (text[i], 80, g) !=NULL) {
    Any guidance on where to go from here would be appreciated.
    Thanks

  2. #2
    Deathray Engineer MacGyver's Avatar
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    Yes, that line will be a problem. Where are you reading the data to? text[i], naturally, but what is index i at the time that line is run?

  3. #3
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    What happens when i = 24 and you try to access text[24]?
    Your classic memory access violation. Put test conditions to make sure i stays within bounds (or dynamically allocate more space when you need it).

    If commented what you should change below:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <conio.h>
    #include <string.h> 
    
    char text[23][80];  // you have 23 strings max, each of 80 chars max
    
    int main() {
    	int i, num; 
    	char c[80]; // you have 80 chars max
    	char temp[80]; // ditto
    	FILE *g;
    	
    	printf("Enter file name:\n");
    	gets(c);  // what happens if the user enters more than 79 chars? crash
                          // always use fgets here: fgets(c, sizeof(c), stdin)
    	g = fopen(c, "r"); 
    	
    	if(g == NULL) {
    		printf("Error: File did not open");
    		exit(0);
    	}
    	while(fgets (text[i], 80, g) !=NULL) {   //perform check to make sure 0 <= i < 80
    		i++; // use ++i, more effecient
    		/* started getting the microsoft send/dontsend error here */
    	}
    	fclose(g);
    	system("cls");  
    	
    	for(i=0; i<23; i++) { // ++i
    		printf("&#37;s", text[i]);
    	}
    	printf("Command:");
    	sscanf(temp, "%c %d", &c, &num);  //c, or &c[0], not &c (c is an array of chars, a.k.a pointer-to-char)
    	
    	while(temp != "Q") {  // NOT the way to compare strings, use strcmp()
    		if(temp == "R") { // ditto
    			fgets(text[num],80,stdin); //again, is num in bounds?
    		}
    		if(temp == "D") {// strcmp()
    			for(i=21; i<num; i++) {  /*"loop from num to 21"...should it be a while loop?? */
     //++i, for loop is fine, but you may want i=num; i < 21
    				strcpy(text[i], text[i+1]);
    				/* "\n" (line 22) ??? */ 
    			}
    		}
    		if(temp == "I") {// strcmp()
    			for(i=22; i>num; i--) { // --i
    				strcpy(text[i], text[i-1]);
    			}
    		}
    		if(temp == "S") {// strcmp()
    			for(i=0; i<23; i++) {// ++i
    				fprintf(g, text[i]);
    			}
    		}	
    	} 	     		
    }
    Since I noticed you are comparing your strings using equalities, maybe you want to read your intro book on C a bit more...
    Last edited by @nthony; 05-30-2007 at 01:29 AM.

  4. #4
    Woof, woof! zacs7's Avatar
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    Quote Originally Posted by @nthony
    i++; // use ++i, more effecient
    Really?

  5. #5
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    I can't tell if that was sarcastic or not... but for the sake of humouring:
    i++ tells the compiler to "use" the value of i and then increment it
    ++i tells the compiler to increment i then "use" its value.
    The difference is, in the former, a temporary variable must be setup for i to hold the original value, then i is incremented and the original value is used in the expression. Whereas in the latter, i is incremented as is, and used in teh expression. Code wise, here is how "a = b + i++" would work:
    Code:
    i_temp is created and set to the value of i (name is really anonymous)
    i is incremented
    b + i_temp is evaluated and stored into a
    now with "a = b + ++i":
    Code:
    i is incremented
    b + i is evaluated and stored into a
    You save yourself extra memory and time. And these effects are double-fold when working with object oriented programs (i.e C++) as allocation of temp vars is much more involved. Especially if you're using i as an auto-incrementer in a for loop (n times faster/more effecient).
    I think there's more about it in the FAQs somewhere though.
    Last edited by laserlight; 05-30-2007 at 02:19 AM. Reason: Fixed a closing code bbcode tag.

  6. #6
    Woof, woof! zacs7's Avatar
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    nah, wasn't sarcastic. Thanks for that

    I've just always read there is 'no real difference' and your free to use any one as you wish.

  7. #7
    C++ Witch laserlight's Avatar
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    I've just always read there is 'no real difference' and your free to use any one as you wish.
    With an optimising compiler, there should be no real difference in this case.
    C + C++ Compiler: MinGW port of GCC
    Version Control System: Bazaar

    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  8. #8
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    Ok, thanks for the suggestions to fix my program.
    Initialising i=0 solved the send/don't send error.
    I was particularly silly not to use the strcpy function, so thanks for pointing that out to me! hehe

    Now when I run my program, I can input the file, get the text from junk.txt to list in the screen, then it will prompt me for a "command:" this is where my next problem is - It will not let me input anything, even though I have a sscanf there :S
    So I'm guessing I still have a problem with my sscanf line: (I have updated it, to how I think you meant it should look anthony)
    Code:
    sscanf(temp, "&#37;c %d", c, &num);
    What have I done wrong? How come it won't let me input anything even with this function in place?

    Thanks again!

  9. #9
    Woof, woof! zacs7's Avatar
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    sscanf() parses a string, you have to read the string from stdin yourself first however.

    You want:
    Code:
    fgets(temp, sizeof(temp), stdin);
    sscanf(temp, "&#37;c %d", c, &num);

  10. #10
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    Quote Originally Posted by zacs7 View Post
    sscanf() parses a string, you have to read the string from stdin yourself first however.

    You want:
    Code:
    fgets(temp, sizeof(temp), stdin);
    sscanf(temp, "%c %d", c, &num);
    That did the trick as far as letting me input text into command. But after I input text, eg Command: "I 6" ... nothing happens, I hit enter and it just stops. According to my program, I should be able to input a line of text to insert after I enter the command, but it just stops.
    I thought my if statement for "Insert (I)" would pick this up:
    Code:
    if(strcmp(temp, "I") ==0) {
    			for(i=22; i>num; i--) {
    				strcpy(text[i], text[i-1]);

    I keep going through it, but I can't see what the heck I've done wrong.
    Thanks

  11. #11
    Woof, woof! zacs7's Avatar
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    no, a strcmp() of "I 6" and "I" won't work since they don't match. Consider comparing 'c' to I, such that
    Code:
    if(c == 'I')
    {
        /* blah */
    Also add some error checking to sscanf(), Hint: It returns the amount of 'parameters' it was able to read.

  12. #12
    Woof, woof! zacs7's Avatar
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    Just remember it's case sensitive!,

    consider, (isupper from ctype.h)
    Code:
    if(toupper(c) == 'I')
    {
         /* blah */
    If you want to match 'i' and 'I'.

  13. #13
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    Quote Originally Posted by zacs7 View Post
    no, a strcmp() of "I 6" and "I" won't work since they don't match. Consider comparing 'c' to I, such that
    Code:
    if(c == 'I')
    {
        /* blah */
    Also add some error checking to sscanf(), Hint: It returns the amount of 'parameters' it was able to read.

    In an earlier post, I was told to replace what I had in my original code with a strcmp, which I did, and now you're telling me not to use the strcmp - I'm getting conflicting responses here Anyways, when I tried using:
    Code:
    if(c == 'I')
    {
        /* blah */
    it returned errors: :50: error: ISO C++ forbids comparison between pointer and integer

    Can anyone help?

  14. #14
    Woof, woof! zacs7's Avatar
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    Code:
    char c;
    if(toupper(c) == 'I')
    {
         /* blah */
    My bad, c isn't needed as a char array anyway, unless your command is more than 1 character...

    Anyway, You should use strcmp() if you want to compare strings, BUT you "I\0" is certainly not equal to "I 6\0" where '6' is your parameter (num)...

    Consider, If you enter "I 6"
    Comparing "I" to "I 6" isn't going to work, the string isn't "I" it's "I <num>"

    Basically:
    Code:
    if(strcmp("I 6", "I") == 0) {
    And they don't match...

  15. #15
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    I understand what you mean, about how they won't match, because of the number there, but how do I go about fixing that? I continue using strcmp? What do I add to it? Sorry, I'm very confused now

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