C：pthread segfaults

Question

I am writing my first C program using pthread. I want to run my function sha1sum for all (non-option) arguments provided on the commadline (argv).

pthread_t t[256];

c = 0;
for (n = optind; n < argc; n++) {
    if(pthread_create(&t[c], NULL, sha1sum, argv[n])) {
        fprintf(stderr, "Error creating thread\n");
        return 1;
    }
    c++;
}

c = 0;
for (n = optind; n < argc; n++) {
    pthread_join(t[c]);
    c++;
}

When run my program with 2 commandline arguments ( file1 , file2 ). it segfaults, sometimes right away, sometimes at the end after having successfully executed the sha1sum function.

Can somebody please point out what is wrong?

EDIT

Turns out, the program is still sometimes segfaulting. Sometimes right away, sometimes in the middle, sometimes never:

I am posting the whole MCV example below:

#include <stdio.h>
#include <getopt.h>
#include <unistd.h>
#include <locale.h>
#include <pthread.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <openssl/evp.h>    

static unsigned char flag = 0;


int sha1sum(char *filename) {

    FILE *f;
    size_t len;
    unsigned char buffer[BUFSIZ]; 

    EVP_MD_CTX hashctx;
    OpenSSL_add_all_algorithms();
    ERR_load_crypto_strings();

    const EVP_MD *hashptr = EVP_get_digestbyname("SHA1");

        f = fopen(filename, "r");

        EVP_MD_CTX_init(&hashctx);
        EVP_DigestInit_ex(&hashctx, hashptr, NULL);

        do {
                len = fread(buffer, 1, BUFSIZ, f);
                EVP_DigestUpdate(&hashctx, buffer, len);
        } while (len == BUFSIZ);

        unsigned int outlen;
        EVP_DigestFinal_ex(&hashctx, buffer, &outlen);
        EVP_MD_CTX_cleanup(&hashctx);

        int i;
        for (i = 0; i < outlen; i++)
                printf("%02x", buffer[i]);

        printf("\n");
        fclose(f);

    pthread_exit(NULL);
}


int main(int argc, char **argv) {

    int c,n;
    pthread_t t[256];

    while ((c = getopt(argc, argv, "c")) != EOF) switch(c) {
        case 'c':
            flag |= 1;
            break;
    }

    c = 0;
    for (n = optind; n < argc; n++) {

        if (pthread_create(&t[c], NULL, &sha1sum, argv[n])) {
            fprintf(stderr, "Error creating thread\n");
            return 1;
        }
        c++;
    }

    c = 0;
    for (n = optind; n < argc; n++) {
        pthread_join(t[c], NULL);
        c++;
    }

    return 0;
}

EDIT 2

after adding #include <pthread.h> , I now get following errors/warnings when compiling:

test.c: In function ‘main’:
test.c:67:9: warning: passing argument 3 of ‘pthread_create’ from incompatible pointer type [enabled by default]
In file included from test.c:9:0:
/usr/include/pthread.h:225:12: note: expected ‘void * (*)(void *)’ but argument is of type ‘int (*)(char *)’

Answer 1

将pthread_join(t[c])更改为pthread_join(t[c], NULL)

Answer 2

I made some small changes to your code. Now it doesn't crash.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <getopt.h>

void *sha1sum(void) {
    char *a = malloc(10);
    strcpy(a, "hello world\n");
    pthread_exit((void *) a);
}

int main(int argc, char **argv) {
    pthread_t t[256];
    int n = 0;
    int c = 0;
    char *b;
    for (n = optind; n < argc; n++) {
        if (pthread_create(&t[c], NULL, &sha1sum, argv[n])) {
            fprintf(stderr, "Error creating thread\n");
            return 1;
        }
        c++;
    }
    c = 0;
    for (n = optind; n < argc; n++) {
        pthread_join(t[c], (void **) &b);
        printf("b is %s", b);
        c++;
    }
    return 0;
}

Test

./a.out foo bar baz bletch
b is hello world
b is hello world
b is hello world
b is hello world