CODEWITHSUNDEEP
cmultithreadingcasting
ThreadedLemon
ThreadedLemon

Reputation: 489

Integer Casting Issue with Multi-threading in C

I am trying to write a simple multi-threaded program that sends a command line argument (an int) to a function, but I am having trouble converting it properly. Below is a snippet of my program excluding irrelevant code.

int main(int argc, char **argv)
{
    pthread_t thread1;
    pthread_create(&thread1, NULL, simple_function, (void*)argv[1]);
    pthread_join(thread1, NULL);
    return EXIT_SUCCESS;
}

void* simple_function(void* num)
{
    int n = *(int *)num;
    printf(The number is: '%d', n);
    n - 1;
    ...
}

What my program actually does:

Command line input: 14

Expected 'printf' result: 14

Actual 'printf' result: 1476408369

There is something missing in my conversion but I am not sure what I should convert it to. There are no warnings during compilation, any help would be greatly appreciated.

Upvotes: 0

Views: 76

Answers (1)

Amleth
Amleth

Reputation: 131

The main thing that stands out is that argv[1] is actually a (char *) not an (int *). You need to convert the string into a numeric value using something like atoi. 

void* simple_function(void* val)
{
    char * c = (char *)val;
    int n = atoi(c);
    printf(The number is: '%d', n);
    n - 1;
    ...
}

Note i have not actually tested the above code as i don't currently have access to a C compiler

Upvotes: 4

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