This should fill the linked list from a file called "data.txt". For some reason it only fills in the first one. Why?Code:datafile=fopen("data.abd","r"); if(datafile!=NULL){ firstp=malloc(sizeof(struct person)); currentp=firstp; while(1){ newp=malloc(sizeof(struct person)); fread(currentp,sizeof(currentp),1,datafile); if(currentp->next==NULL){ break; } currentp->next=newp; currentp=newp; } fclose(datafile); }
~Sven
Windows XP Home Edition - Dev-C++ 4.9.9.2
board.theprogrammingsite.comOriginally Posted by "The C Programming Language" by Brian W. Kernignhan and Dennis M. Ritchie
malloc does not null its values when called. All it does is give you a pointer to some place in memory. Just like local non-static variables, they're unintialized upon creation, and contain some random data. That said, you're doing this pretty much ass backwards.
You should be looping based on the return value of fread, not on if what you've happened to read has somehow magically set the 'next' pointer to NULL or not.
Quzah.
Hope is the first step on the road to disappointment.
This is from a file that was already printed from a linked list. I make the linked list in my program and then fwrite it into "data.txt" and read it back next time the program is run. So if currentp->next was NULL when it was printed into the file shouldn't it be NULL when it comes back out?
~Sven
Windows XP Home Edition - Dev-C++ 4.9.9.2
board.theprogrammingsite.com
[edit]
Change your if() to test the return value of fread(), as suggested by Quzah.
[/edit]
Last edited by dwks; 04-21-2006 at 03:53 PM.
dwk
Seek and ye shall find. quaere et invenies.
"Simplicity does not precede complexity, but follows it." -- Alan Perlis
"Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
"The only real mistake is the one from which we learn nothing." -- John Powell
Other boards: DaniWeb, TPS
Unofficial Wiki FAQ: cpwiki.sf.net
My website: http://dwks.theprogrammingsite.com/
Projects: codeform, xuni, atlantis, nort, etc.
But I read the structure from the file into currentp. So doesn't it have that stuff in it?
~Sven
Windows XP Home Edition - Dev-C++ 4.9.9.2
board.theprogrammingsite.com
You might want sizeof(*currentp).Code:fread(currentp,sizeof(currentp),1,datafile);
dwk
Seek and ye shall find. quaere et invenies.
"Simplicity does not precede complexity, but follows it." -- Alan Perlis
"Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
"The only real mistake is the one from which we learn nothing." -- John Powell
Other boards: DaniWeb, TPS
Unofficial Wiki FAQ: cpwiki.sf.net
My website: http://dwks.theprogrammingsite.com/
Projects: codeform, xuni, atlantis, nort, etc.
Oh, I had that in my program I must have mistyped it into here. How do I make this work though?
~Sven
Last edited by 00Sven; 04-21-2006 at 04:00 PM.
Windows XP Home Edition - Dev-C++ 4.9.9.2
board.theprogrammingsite.com
OK I got it. I read through my program a few times and realized that I was writing the entries to the file as soon as they were made. So they were the last entries causing their pointer to be NULL when in the file so it stopped at the first one everytime. Stupid mistake.
~Sven
Windows XP Home Edition - Dev-C++ 4.9.9.2
board.theprogrammingsite.com
> Oh, I had that in my program I must have mistyped it into here. How do I make this work though?
Here's a tip - use copy/paste of your actual code.
Simply typing here what you think you have isn't good enough. You only need to be off by a very small number of characters before the advice goes off in a completely different direction to your actual problem.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
