Sum of words using threads - c

Question

Problem: Implement a program that gets as arguments a file name followed by words. For each word, create a separate thread that counts its appearances in the given file.Print out the sum of the appearances of all words.
Below I did a code but I receive : Segmentaion Fault (core dumped) when I run it.
PS: I do not know if the code is correct and does the requirement succesfully
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
pthread_mutex_t mtx;
int sum = 0;
char filename[10];
char word[10];
void * voidCount(void* p){
char cmd[100], appearences[100];
FILE *f;
sprintf(cmd, "echo %s | grep -o %s | wc -l", filename, word);
f = popen(cmd, "r");
fgets(appearences, sizeof(int), f);
pthread_mutex_lock(&mtx);
sum += *((int*)appearences);
pthread_mutex_unlock(&mtx);
return NULL;
}
int main(int argc, char *argv[]){
pthread_mutex_init(&mtx, NULL);
pthread_t threads[argc-1];
int i = 0;
for ( i = 1; i < argc-1; i++){
strcpy(filename, argv[1]);
strcpy(word, argv[i]);
pthread_create(&threads[i], NULL, voidCount, NULL);
}
for (i = 0; i < argc-1; ++i){
pthread_join(threads[i], NULL);
}
printf("Total appearences: %d", sum);
pthread_mutex_destroy(&mtx);
return 0;
}

Answer 1

The program has to complete few tasks in order to solve the problem:
set the number of threads depending on the number of words to search for
properly allocate and initialize thread arguments
pass each individual word as individual thread argument
protect shared variables during computation
get the results
Here's a minimal functional demo rework of your code with few essential comments. Word search is case sensitive.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
pthread_mutex_t mtx;
int sum = 0;
char filename[10]; //declared global for simplicity
//we search all the words in the same file
void * voidCount(void* p){
char *word, cmd[100], appearences[100];
int num;
FILE *f;
word = ((char*)p);
printf ("word : %s\n",word);
sprintf(cmd, "more %s | grep -o %s | wc -l", filename, word);//echo didn't work
printf ("%s\n",cmd); //debug print
pthread_mutex_lock(&mtx);
f = popen(cmd, "r");
if(fgets(appearences, sizeof(appearences), f) == NULL)
printf("Pipe error\n"); //better error handling is welcome...
printf("Appearances of \"%s\": %s\n", word, appearences);
num = atoi(appearances); //convert string to int
sum += num;
pclose(f); //close pipe
pthread_mutex_unlock(&mtx);
return NULL;
}
int main(int argc, char *argv[])
{
pthread_mutex_init(&mtx, NULL);
pthread_t threads[argc-1];
char **data = calloc(argc,sizeof(char*)); // initialize thread data
int i = 0;
strcpy(filename, argv[1]);
for ( i = 2; i < argc; i++){
data[i-2] = calloc(33, sizeof(char));//let's allow for somewhat longer words
strcpy(data[i-2], argv[i]);
strcat(data[i-2], "\0");
pthread_create(&threads[i-2], NULL, voidCount, data[i-2]);//each word a thread arg
}
for (i = 0; i < argc-1; ++i){;
pthread_join(threads[i], NULL);
}
printf("Total appearences: %d\n", sum);
pthread_mutex_destroy(&mtx);
for (i = 0; i < argc; i++)//free thread data
free (data[i]);
free (data);
return 0;
}
Hope this can help.