I need an explanation with File I/O I am recieving warnings I do not understand - linux

Question

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <string.h>
struct string_count_struct{
char fname;
char str;
long long count;
};
void* filesearch(void* arg)
{
//get the file name
struct string_count_struct *arg_ptr = (struct string_count_struct*) arg;
int line_num = 1;
int find_result = 0;
char temp[512];
//create a file pointer
FILE *fp;
fp = fopen(arg_ptr -> fname, "r");
//dont forget error handling
if (fp == NULL){
printf("File could not be opened");
return(-1);
}
while (fgets(temp, 512, fp) != NULL) {
if ((strstr(temp, arg_ptr -> str)) != NULL) {
find_result++;
}
line_num++;
}
if(find_result = 0) {
printf("\nSorry, couldn't find a match.\n");
}
arg_ptr -> count = find_result;
//close the file
if (fp){
fclose(fp);
}
pthread_exit(0);
}
int main (int argc, char **argv)
{
if (argc < 3) {
printf("Usage: <file> <string> <arg1> <arg2>...<argN>\n", argv[0]);
exit(-1);
}
int num_args = argc - 2;
struct string_count_struct args[num_args];
//Thread Creation:
pthread_t tids[num_args];
for(int i = 0; i < num_args; i++) {
args[i].fname = atoll(argv[i + 2]);
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_create(&tids[i], &attr, filesearch, &args[i]);
}
//Wait until work is completed
for (int i = 0; i < num_args; i ++){
pthread_join(tids[i], NULL);
printf("blah is blah %lld\n", args[i].count);
}
return 0;
}
Here are my warnings
root#kali:~/Desktop# gcc prog2.c -lbthread
prog2.c: In function ‘filesearch’:
prog2.c:29:13: warning: passing argument 1 of ‘fopen’ makes pointer from integer without a cast [-Wint-conversion]
fp = fopen(arg_ptr -> fname, "r");
^~~~~~~
In file included from prog2.c:1:0:
/usr/include/stdio.h:274:14: note: expected ‘const char * restrict’ but argument is of type ‘char’
extern FILE *fopen (const char *__restrict __filename,
^~~~~
prog2.c:34:8: warning: return makes pointer from integer without a cast [-Wint-conversion]
return(-1);
^
prog2.c:38:21: warning: passing argument 2 of ‘strstr’ makes pointer from integer without a cast [-Wint-conversion]
if ((strstr(temp, arg_ptr -> str)) != NULL) {
^~~~~~~
In file included from prog2.c:4:0:
/usr/include/string.h:337:14: note: expected ‘const char *’ but argument is of type ‘char’
extern char *strstr (const char *__haystack, const char *__needle)
^~~~~~
prog2.c: In function ‘main’:
prog2.c:78:17: error: assignment of read-only member ‘fname’
args[i].fname = atoll(argv[i + 2]);
I am unsure of what I am doing wrong, these errors are preventing my program from correctly reading through the desired files and calculating the # of occurrences of a particular string that the user will select. I have fixed my error but not the warnings.
The program will take a command line argument, create a separate thread for each file to be searched through, search through each file, and then give the results. I plan on using a Mutex for further refinement, but right now I am just trying to solve my I/O issues.

Answer 1

Just addressing some of the warnings, I'm not at all sure if this will make the code work:
In line 29, fopen expects a filename (char *) but fname is just a char in string_count_struct. Make it a char*. In the main function you convert one of the arguments from ASCII to long long and assign it to fname, which shall later be used as a file name for fopen(). That's probably not what you want to do.
In line 34, you return -1 which is not a pointer. You declared the function to be returning a void pointer. Make it return(0) (or return(NULL)).
Same as in line 29 happens in line 38: str in the struct string_count_struct is just a char, but strstr expects a char*. Make it a char*, too.
Your "Usage" is missing a "%s" format string to actually print the argument argv[0].