Segmentation Fault when using Structures and pThreads - c++

Question

I have been working with a program that will read through multiple text files, record the number of words in them, and write to a file all of the words and the frequency of them. However, I have encounter a segmentation fault somewhere in my code. I have tried using tools such as Valgrind to help me debug it, however it only points to where I say int i = 0 in the main loop. I apologize for posting a large portion of my code but I have spent hours trying to find where the bug is and cannot seem to find it for the life of me. The issues began when I started passing a structure in pthread_exit().
#include <iostream>
#include <fstream>
#include <string>
#include <pthread.h>
#include <vector>
#include <algorithm>
#include <sstream>
#include <iterator>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <cstdio>
using namespace std;
// Create a structure that we can store information in
typedef struct info{
int words;
string dictionary[500000];
} info;
// Counts the number of words in the text file so we know how big to make our array
int countWord(char *arg){
char words[25000];
int count = 0;
ifstream check;
check.open(arg);
while(!check.eof()){
check>>words;
count++;
}
cout<<"Word Count: "<< count << '\n';
check.close();
return count;
}
// Checks to see if the word exists in our dictionary or not
int findWord(string array[], string target, int wordCount){
for(int i = 0; i < wordCount; ++i){
if(array[i] == target){
return 1;
}
}
return 0;
}
// Checks to see how many times a word is repeated
int checkWord(string array[], string target, int wordCount){
int number = 0;
for(int i = 0; i < wordCount; i++){
if(array[i] == target){
number++;
}
}
return number;
}
void *threads(void *arg){
info information;
char *fileName = (char *)arg;
ifstream myfile (fileName);
string line;
string fullText[15000];
string dictionary[500000];
int wordCount = countWord(fileName);
int i = 0;
int find;
int check;
int x = 0;
int checkingStart = 0;
// Opens and reads the file word by word removing any symbols that we dislike
if (myfile.is_open()){
while(myfile >> line){
transform(line.begin(), line.end(), line.begin(), ::tolower);
line.erase(remove(line.begin(), line.end(), ','), line.end());
fullText[i] = line;
i++;
}
}
else cout << "Unable to Open the File";
myfile.close();
// Goes through and adds all the words to our dictionary
for(i = 0; i < wordCount; ++i){
find = findWord(dictionary, fullText[i], wordCount);
if(find == 0){
dictionary[x] = {fullText[i]};
++x;
checkingStart = 1;
}
}
// Sets each section of dictionary equal to the one in the structure
for(i = 0; i < wordCount; ++i){
information.dictionary[i] = dictionary[i];
}
// Sets words equal to word count and then passes the structure information out of the thread
information.words = wordCount;
pthread_exit(&information);
return NULL;
}
int main(){
int i = 0;
int x = 0;
int y = 0;
int z = 0;
int a = 0;
int b = 0;
int add = 0;
int currentSize = 0;
int checkingStart = 0;
int wordCount;
int find;
string fullDictionary[500000];
string dict[500000];
ofstream writeFile;
info information;
char *fileName;
char *fileList[2];
pthread_t threadCount[2];
int frequency[500000];
int check;
fileList[0] = "text1";
fileList[1] = "text2";
// Creates a loop that creates and joins threads for each text file
for(a = 0; a < 1; ++a){
fileName = fileList[a];
pthread_create(&threadCount[a], NULL, threads, &fileName);
pthread_join(threadCount[a], (void **)&information);
wordCount = information.words;
// Sets each part of dict equal to the same slot on info.dict
for(b = 0; b < wordCount; ++b){
dict[b] = information.dictionary[b];
}
// Adds to a complete list of all the text files added together
for(y = 0, z = currentSize; z < wordCount; ++z, ++y){
fullDictionary[z] = dict[y];
}
currentSize = (currentSize + wordCount);
}
// Goes through and adds all the words to our dictionary
for(i = 0; i < wordCount; ++i){
find = findWord(dict, fullDictionary[i], currentSize);
if(find == 0){
dict[x] = {fullDictionary[i]};
cout << "Added the Word: " << fullDictionary[i] << "\n";
add = 1;
checkingStart = 1;
}
// Checks the number of times each word appears in the text file
if(checkingStart == 1){
check = checkWord(fullDictionary, dict[x], wordCount);
frequency[x] = {check};
}
// Checks to see if it needs to move to the next open dictionary spot
if(add == 1){
++x;
add = 0;
}
}
return 0;
}

Answer 1

These were the changes that were needed to get the program working.
1) One issue seems to be that the size of the variables in the function threads. Looks like every thread that is spawned has some default limit . You could read up on pthread_attr_setstacksize. but the simplest solution was to reduce the size of the strings in thread.So the size of the variables are why it's gives a segmentation fault as soon as the threads function is called.
As already mention in the comments above usage of vector/maps classes will help reduce the need for large local variables.
2) The return variable needs to be a non-local variable else the return value does not make it back successfully.
3) just noticed the main loop ( variable a ) is running only once . Also once the thread is launched(pthread_create) the loop is waiting for the join . This will result in serialization of the threads. The create can be done first and then the join can be in called in a separate loop after that.
Changes are given below ..
In function - threads
info *information;
//changed to pointer
// info information;
char *fileName = (char *)arg;
ifstream myfile (fileName);
string line;
string fullText[1500];
string dictionary[5000];
// reduced size
//string fullText[15000];
//string dictionary[500000];
.....
information = new info; // create an instance
........
// change to pointer
information->dictionary[i] = dictionary[i];
}
// Sets words equal to word count and then passes the structure information out of the thread
information->words = wordCount;
pthread_exit(information); // return pointer
in function - main
info *information; // change to pointer
....
for(a = 0; a < 2; ++a){ // loop to 2
.....
pthread_create(&threadCount[a], NULL, threads, (void *)fileName); // changed file name
// pthread_create(&threadCount[a], NULL, threads, &fileName);
wordCount = information->words; // changed for pointer
...
dict[b] = information->dictionary[b] // changed for pointer
After the edits you should be able to run to debug the rest of the functionality.