Question

I was so pleased with myself getting this to work last night without any errors or warnings on my first try too! But, of course, I changed a bunch of stuffed and screwed it up…
When I tried to gdb it, the list from this.ytxt seemed load to memory just fine. I think the problem was writing it. Now. it works again but only writes the first line of the file. I commented out whole functions and printf’d test marks and still couldn’t figure it out.
the idea is to read a variable number of lines from a file and print them in pairs. (Actually
it was meant to be like study flashcards but I never got around to that part)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct member{      //This emulates a dictionary
    char key[20];   //and links each word+definition pair to the next pair.
    char def[20];
    struct member *ptr;
};
struct member *root;
struct member *curr;
FILE *f;

int fill_list(){                //Fill each member struct with next two lines of
    curr=root;
    char this[20];              //FILE *f
    while(EOF){
        if(!fgets(this,20,f)) break;
        strcpy(curr->key,this);
        if(!fgets(this,20,f)) break;
        strcpy(curr->def,this);
        curr=curr->ptr;
        curr=malloc(sizeof(struct member));
        curr->ptr=0;
    }
    return 0;
}

void free_all(){
    curr=NULL;
    while(curr!=root){
        curr=root;
        while(curr->ptr)curr=curr->ptr;
        free(curr);
    }
}

 int terminate(int i){  //The terminate function closes file and
    free_all(); //frees malloc'd memory, then returns main func's
    fclose(f);  //return value.
    return i;
}

int main(){
    f=fopen("this.txt","r");
    if(!f)return -1;
    root=malloc(sizeof(struct member));
    root->ptr=NULL;
    fill_list();
    curr=root;
    if ( curr != 0 ) {
      while ( curr != 0 ) {
        printf( "%s", curr->key );
        curr = curr->ptr;
      }
    }
    free_all();
    return terminate(0);
}

Answer 1

Elaborating on Chad’s answer, you could have:

int fill_list(){                //Fill each member struct with next two lines of
    struct member *new_mem;
    curr=root;
    char this[20];              //FILE *f
    while(1){ /* relying on the breaks below to exit the loop */
        if(!fgets(this,20,f)) break;
        strcpy(curr->key,this);
        if(!fgets(this,20,f)) break;
        strcpy(curr->def,this);
        /* create the new member */
        new_mem=malloc(sizeof(struct member));
        /* set the new member's next ptr to NULL */
        new_mem->ptr = NULL;
        /* set the current member's next to the new member */
        curr->ptr=new_mem;
        /* current is now the new member */
        curr = new_mem;
    }
    return 0;
}

EDIT: thought I’d just add that if I was going to make slight modifications to your code this is what I’d do. If I were to do it from scratch I wouldn’t structure the loop that way or have unnecessary global variables like curr. Same goes for the point made by sarnold where you only have a single temporary buffer. Not to mention that your last entry in the list could be invalid; it might be a better idea to allocate the next member entry in the list only after you successfully read the two strings into two temporary buffers.