print a text-file in linked list

This is a discussion on print a text-file in linked list within the C Programming forums, part of the General Programming Boards category; I need to get a C program to read a text-file (with aprox. 4 lines) to a linked list. and ...

  1. #1
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    print a text-file in linked list

    I need to get a C program to read a text-file (with aprox. 4 lines) to a linked list. and print it out.

    A simple method of doing this:
    Code:
    char c[10];
      FILE *file;
      file = fopen(argv[1], "r"); 
      if(file==NULL) {
        printf("Can not open file.\n");
        return 1;
      }
    while(fgets(c, 10, file)!=NULL) { 
          	printf("%s", c);
          }
          printf("\n");
    Although this example do not use struct or lists, which is what I need. It should look something like this:
    First, create the struct before main().
    Code:
    struct sang {
    struct sang *neste;
    char linje[200];
    int ant;
    };
    Then allocate memory in main():
    Code:
    struct sang *liste = malloc(sizeof(struct sang));
    Then open the text-file from argv[1] and put into the struct.
    Code:
     
    char c[10];
      FILE *file;
      file = fopen(argv[1], "r"); 
      if(file==NULL) {
        printf("Can not open file.\n");
        return 1;
    printf("testing %s",strcpy(liste.linje[200],argv[1]));
    The last line is my own invention. Which doesn't work. If anyone can point me in the right direction I would really appreciate it!

  2. #2
    ATH0 quzah's Avatar
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    You're using strcpy wrong. More importantly, you're passing arrays to functions incorrectly. When you pass an array, like when you want to use strcpy, just pass the name of the array. Also, assuming 'liste' is actually a pointer, and not just a structure instance, you're accessing its members incorrectly. To access structure members via pointer, you need the "arrow" operator.
    Code:
    strcpy( liste->linje, argv[1] );
    Of course that's not getting anything from your file. It's just copying your file name (assuming that's what is in argv[1]) into your list.


    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
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    Ok! Thanks for the help. I've been working a couple of hours more now and figured some things out. A simplified code piece:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    #define MAX 2000
    #define LENGTH 200
    
    struct song {
      struct song *next;
      char *line;
    };
    
    int main(int argc, char *argv[])
           struct song *list = NULL, *last = NULL, *pdp;
    	pdp = malloc(sizeof(struct song));
           int n_lines;
           char *ant;
    
    /* Check if file can be opened*/
      	char c[10];
      	FILE *file;
      	file = fopen(argv[2], "r"); 
      	  if(file==NULL) {
        	    printf("Error: Can't open file.\n");
        	    exit(1);
      	  }   
    	
    /* Copy the text into list */
    	while (1) {
    	  ant = malloc(LENGTH );
    	    if (fgets(ant,LENGTH ,file) == NULL) {
    	      free(ant); break;
    	    }
    	  pdp->next = NULL; pdp->line = malloc(*ant);
    	  strcpy(pdp->line, ant);
    	    if (list == NULL) {
    	       list = last = pdp;
    	    } else {
    	      last->next = pdp; 
    	      last = pdp;
    	    }
    	}
    /* Print the list */
    	pdp = liste;
    	  while (pdp) {
    	    printf("%s\n", pdp->line);
    	    pdp = pdp->next;
    	  }
    I can figure out why the output prints the last line in the text-file infinite times (only stopped by CTRL+C). I think it has something to do with "fgets" but I maybe wrong.
    Last edited by tidemann; 09-19-2006 at 03:26 AM.

  4. #4
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    Where are you declaring ant_line?

    And pdp->line = malloc(*ant); is wrong. You want malloc(strlen(ant->line) + 1) instead.
    Last edited by itsme86; 09-18-2006 at 08:39 AM.
    If you understand what you're doing, you're not learning anything.

  5. #5
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    Ops! ant_line should be ant (edited now).. just a typo. If I use malloc(strlen(ant->line) + 1) i get the following error:

    "request for member 'line' in something not a structure or union"

  6. #6
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    Well is ant a pointer to a structure or union?
    System: Debian Sid and FreeBSD 7.0. Both with GCC 4.3.

    Useful resources:
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  7. #7
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    It should be a pointer to a struct(ure). I'm a newbie when it comes to creating single-lists in structures.

    First I thought that...
    Code:
      if (fgets(ant,LENGTH ,file) == NULL) {
    	      free(ant); break;
    	    }
    ... disturbed the input with actually writing a line into the list which shouldn't be there. It maybe another problem though...

  8. #8
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    Quote Originally Posted by tidemann
    It should be a pointer to a struct(ure).
    If that's what it should be, why did you declare it as pointer-to-char?
    System: Debian Sid and FreeBSD 7.0. Both with GCC 4.3.

    Useful resources:
    comp.lang.c FAQ | C++ FQA Lite

  9. #9
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    Since ant is working with the concurrent object in the list I thought that it should be a char* since it will contain text . The fgets-example I posted above won't work if its declared as anything else. Nor would strcpy. Should it be declared as something else?

  10. #10
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    I solved the problem. I just had to re-write most of the copying... If anybodys interested I'll post the finished code at demand

  11. #11
    and the hat of wrongness Salem's Avatar
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    One of you malloc calls needs to go - you don't need both.

    Option 1 - read into array, then allocate space and copy
    char buff[BUFSIZ]; fgets( buff, sizeof buff, file );
    pdp->line = malloc(strlen(buff)+1);
    strcpy(pdp->line, ant);

    Option 2 - allocate space, read in a line then save the pointer
    ant = malloc(LENGTH );
    fgets(ant,LENGTH,file)
    pdp->line = ant;
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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