CODEWITHSUNDEEP
c++c++11pointersqueue
kittydoor
kittydoor

Reputation: 123

Why is my simple C++ program working with queue and fstream erroring out into invalid pointer?

Here is a github gist of the code, if preferred I can append the code to this question too.

https://gist.github.com/alevnyaa/e917bc2aa1e72aa210d8cff9fa5e922b

When I compile and run this program with g++ 6.3 with c++11 on linux, after working through the first few lines the program crashes after print_queue is called at line 62. As I am not even manually working with pointers or memory, I have no idea what the problem here is.

*** Error in `./a.out': free(): invalid pointer: 0x0000000000606160 ***

I can try any suggestions. I am assuming that I am not noticing a simple problem, but I am blinded after looking at it too many times.

Thank you

Here is the code:

Firstly the file D301.txt

D301    Capacity 40

1   1               5
2       2       4   
3           3   4   
4        
5       2           
6        
7   1

ifqueue.cpp

#include <fstream>
#include <iostream>
#include <queue>

void stoq(std::queue<char>& q, std::string s){
  std::queue<char> empty;
  std::swap(q, empty);
  for(char ch : s){
    if(!isspace(ch)){
      q.push(ch);
    }
  }
}

std::string print_queue(std::queue<char> q){
  std::cout << "Queue: ";
  int i = 0;
  while(!q.empty()){
    std::cout << "i" << i;
    i++;
    std::cout << q.front();
    q.pop();
  }
  std::cout << std::endl;
}

int main(){
  std::fstream infile("D301.txt");
  std::string line;
  std::queue<char> q;
  std::getline(infile, line);
  stoq(q, line);

  print_queue(q);

  std::string classroom_name;
  while(q.front() != 'C'){
    classroom_name += q.front();
    q.pop();
  }

  for(int i=0; i<8; i++){
    q.pop();
  }

  std::string capacity_str;

  while(!q.empty()) {
    capacity_str += q.front();
    q.pop();
  }

  int capacity = stoi(capacity_str);

  std::getline(infile, line);
  while(infile){
    std::getline(infile, line);
    std::cout << "fl" << std::endl;
    stoq(q, line);
    std::cout << "sl" << std::endl;
    print_queue(q);
    std::cout << "tl" << std::endl;
  }

  infile.close();
}

Was the -1 really warranted?

Upvotes: 0

Views: 429

Answers (2)

kittydoor
kittydoor

Reputation: 123

I am unsure as to why the error was as such. However, the fix seems to be changing the function:

std::string print_queue

into

void print_queue

As it isn't actually returning a string.

If anyone can pitch in why I was getting that kind of error, I'll be happy to find out.

Upvotes: 1

didiz
didiz

Reputation: 1099

What happens when the queue is empty?

 while(q.front() != 'C'){
        classroom_name += q.front();
        q.pop();
     }

What happens if the queue has less than 8 elements?

for(int i=0; i<8; i++){
    q.pop();
  }

Upvotes: 1

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