Reading random line from a text file

Hello,
I really need help with this program. It's a wheel of fortune program. I think I'm really close to finishing it but I really need help adapting it to read a text file of any length and to make sure that when a random line is chosen from the text file it is not chosen again. Thanks again in advance.

Code:

---

int initialize_array(char phrase[], char puzzle[], char clue[]){
        FILE* phraseFile; /*input file*/
        char temp[100]; /*temporary array*/
        int line; /*line from which word and clue are chosen*/
        size_t i=0; /*counter for loop*/
        int len; /*length of line from file*/


        line=rand()%43+1; /*randomization of line*/
       
        phraseFile = fopen("clues.txt", "r"); /*opens file*/
                   
        if (!phraseFile) {
                fprintf(stderr, "Oops - file not opened !\n"); /*if there is error in opening file program is exited*/
                exit(1);
                }

                while(line--){
                        fgets(temp, 100, phraseFile); /*gets line and stores in temp*/
                }
               
        len=strlen(temp);
        if(temp[len-1]=='\n')
                temp[len-1]=0; /*places the null terminating character after word*/
               
                /*separates clues from word*/
                strcpy(clue,strtok(temp, "%"));
                /*
                strcpy(phrase,strtok(NULL,"%"));*/
        char tmp[WORD_LENGTH];
        strcpy(tmp,strtok(NULL,"%"));
        strcpy(phrase, tmp + 1);
        strcpy(puzzle,phrase);


                /*strcpy(puzzle,phrase);*/
       
                while(i<strlen(puzzle)){
                        if(isalpha(puzzle[i])){
                                puzzle[i] = '*'; /*hides word*/
                                }
                                ++i;
                        }
        fclose(phraseFile);        /*closes file*/       
        return i;
}

---

IMO, your best bet is to do one of the following:

1. Read the entire file into memory line by line, and from there manage which lines are selected.
2. Manage which line is selected internally, and then read to that line in the file.

If the file is not large, use option 1. If the file is huge or you won't be selecting many lines, use option 2.

So to modify my code I would need to do
while(fgets(temp,100, phraseFile)....but then I'm lost as to what I should do after that. I would appreciate any guidance. I really want to get this project done. I've been working on it for weeks (I'm a beginning C student) and things have been really slow. Please help me

Could someone please guide me in how to correct this? Thank you.

Code:

---

int initialize_array(char phrase[], char puzzle[], char clue[]){
        FILE* phraseFile; /*input file*/
        char temp[100]; /*temporary array*/
        int line; /*line from which word and clue are chosen*/
        int i=0; /*counter for loop*/
        int len; /*length of line from file*/
        int count=0;

       
        phraseFile = fopen("clues.txt", "r"); /*opens file*/
                   
        if (!phraseFile) {
                fprintf(stderr, "Oops - file not opened !\n"); /*if there is error in opening file program is exited*/
                exit(1);
                }
               
                while(fgets(temp,100,phraseFile)!=0){
                        ++count;
                }
                       
                line= rand()%count;
       
                while(line--){
                        fgets(temp, count, phraseFile); /*gets line and stores in temp*/
                }
               
        len=strlen(temp);
        if(temp[len-1]=='\n')
                temp[len-1]=0; /*places the null terminating character after word*/
               
                /*separates clues from word*/
                strcpy(clue,strtok(temp, "%"));
                /*
                strcpy(phrase,strtok(NULL,"%"));*/
char tmp[WORD_LENGTH];
        strcpy(tmp,strtok(NULL,"%"));
        strcpy(phrase, tmp + 1);
        strcpy(puzzle,phrase);
 
 
                /*strcpy(puzzle,phrase);*/
       
                while(i<strlen(puzzle)){
                        if(isalpha(puzzle[i])){
                                puzzle[i] = '*'; /*hides word*/
                                }
                                ++i;
                        }
        fclose(phraseFile);        /*closes file*/       
        return i;
}

---

3 things to fix:
- Don't use exit in your function. Return an error instead! It's bad to use exit in a function because you never know if the parent function or any other functions need to perform cleanup work if it fails, or if it can recover.
- fgets wants buffer, sizeof(buffer), file, not buffer, count, file (count being 0! - which means fgets will read nothing or error).
- Don't use strcpy(..., strtok(...)). If strtok returns NULL, you will crash your program! Use strtok first, check for NULL, then copy.

Quote:

---

Originally Posted by Elysia

3 things to fix:
- Don't use exit in your function. Return an error instead! It's bad to use exit in a function because you never know if the parent function or any other functions need to perform cleanup work if it fails, or if it can recover.

---

exit can't do cleanup?

Code:

---

NAME
      exit - cause normal program termination

SYNOPSIS
      #include <stdlib.h>

      void exit(int status);

DESCRIPTION
      The  exit() function causes normal program termination and
      the value of status is returned to the parent.  All  func-
      tions registered with atexit() and on_exit() are called in
      the reverse order of  their  registration,  and  all  open
      streams are flushed and closed.

---

Well, exit may cause functions not to do cleanup or try to recover or print appropriate error messages. It's not recommended to use it.

Thanks for those warnings. However what I'm really trying to focus on is getting the line. After changing fgets(temp, count, phraseFile) to say while(fgets(temp, 100, phraseFile), what else do I need to do to get this code running. Everytime I run my program I get a segmentation fault. Thanks for the help so far.

> Well, exit may cause functions not to do cleanup or try to recover or print appropriate error messages. It's not recommended to use it.


I don't believe it, maybe you could explain or demonstrate?

Well, I mean...

Code:

---

int foo1()
{
    /* Some stuff */
    return ERROR_FAIL;
}

void foo2()
{
    int error = foo1();
    if (error)
        log("Error in foo2 - call to foo1 failed with error: " + error);
}

void foo3()
{
    foo1();
}

---

This code won't compile, of course, but it's enough for demonstration purposes.
I mean, how does foo1 know what its parent function will do?
If it calls exit, then the parent function never gets to execute that code.
Sure, it can be caught with some functions registered with at_exit, but again, how would at_exit know the state of the program? The parent function would know and could handle the error, perhaps even recover, which isn't something that's easy to do if you call exit.

helloamuro:
Take a closer look at the last two lines of advice I offered. They can cause undefined behaviour and crashes if improperly used.

I've made your corrections, but there still is a segmentation fault....

Quote:

---

Originally Posted by Elysia

Well, I mean...

Code:

---

int foo1()
{
    /* Some stuff */
    return ERROR_FAIL;
}

void foo2()
{
    int error = foo1();
    if (error)
        log("Error in foo2 - call to foo1 failed with error: " + error);
}

void foo3()
{
    foo1();
}

---

This code won't compile, of course, but it's enough for demonstration purposes.
I mean, how does foo1 know what its parent function will do?
If it calls exit, then the parent function never gets to execute that code.
Sure, it can be caught with some functions registered with at_exit, but again, how would at_exit know the state of the program? The parent function would know and could handle the error, perhaps even recover, which isn't something that's easy to do if you call exit.

---

True, true. Wouldn't want to start an argument here, but foo1 is poorly designed. If it returns error codes, under what circumstances would it call exit? It seems like you could avoid this whole kludge simply by rewriting the parent function so that it calls exit instead:

Code:

---

#include <stdlib.h>
int child ( void )
{
  return -1;
}

void parent ( void )
{
  if ( child() == -1 ) {
      /** log( "fubar'd" ); **/
      exit( 1 );
  }
  /** ... **/
}

---

If that's not possible, it should be documented behavior, so it's not a mystery that the child function would call exit. In any case, the proper way to use the child function depends on its preconditions. Ensure a return if exit is a problem.

Hope that helps you understand the C library a little better.

1. you probably need to rewind your file before starting the read again
2. temp[len-1] - check that len > 0 before it
3. where tmp is defined?
4. are all passed buffers big enough to store the parts of the string?
5. check the return value of strtok before copying
6. while(i<strlen(puzzle))
better to write
while(puzzle[i])

I can't use rewind (I'm familiar with it, but it hasn't been covered in my class) but would just opening and closing the file again be sufficient?

That's a waste of time (but it could be done). Are you allowed to use fseek then? It can do the same thing.
Otherwise, you can do as MacGyver initially suggested: open the file and read everything into memory and deal with it from there.

The opening and closing seems to be working, but could someone guide or give me a suggestions as to how to store which lines have been used? Perhaps if I stored the indexes?

Quote:

---

Originally Posted by helloamuro

I can't use rewind (I'm familiar with it, but it hasn't been covered in my class) but would just opening and closing the file again be sufficient?

---

If you cannot use rewind or fseek - then fclose/fopen will do the trick

Quote:

---

Originally Posted by helloamuro

The opening and closing seems to be working, but could someone guide or give me a suggestions as to how to store which lines have been used? Perhaps if I stored the indexes?

---

You will need 2 dimantional array - to store each line in one member of this array

Or is there anyway I can just use a flag to tell if the line has been used or not?

I don't really want to use a 2d array because I have been so often criticized for trying to use them before.

I currently have this for getting the line number. What could I add to it to prevent the same one from being used again

Code:

---

while(fgets(temp,100,phraseFile)!=0){
                        ++count;
                }
               
                fclose(phraseFile);
                fopen("clues.txt", "r");
                line= rand()%count;
               
                while(line--){
                        fgets(temp, 100, phraseFile); /*gets line and stores in temp*/
                }

---

seems to be ok except
fopen("clues.txt", "r"); - you need to store the return value again

bytheway - if line == 0 you will be left with the last read line in the buffer...

Would the line ==0 work though if my program is in a loop to be performed three times though? It seems like there could be a change that the first and third rounds of the program could use the same word...

Quote:

---

Originally Posted by Elysia

Otherwise, you can do as MacGyver initially suggested: open the file and read everything into memory and deal with it from there.

---

Whoa, how did I miss this? Elysia agreed with me for once.

/me writes down the date and time. :D

Quote:

---

Originally Posted by helloamuro

Would the line ==0 work though if my program is in a loop to be performed three times though? It seems like there could be a change that the first and third rounds of the program could use the same word...

---

I suppose you need to add line++
before your
while(line--) loop