Problem with passing struct pointer by pthread_create

Question

In the code below, when I print f->msg in the main function, the data prints out correctly. However, if I pass the mystruct *f in pthread_create and try to print out the msg value, I get a segmentation fault on the second line of the receive_data function.

typedef struct _mystruct{
    char *msg;
} mystruct;

void *receive_data(void* vptr){
    mystruct *f = (mystruct*)vptr;
    printf("string is %s\n",mystruct->msg);
    return NULL;
}

int main(){
    mystruct *f = malloc(sizeof(mystruct));
    f->msg = malloc(1000);
    f->msg[0] = '\0';
    strcpy(f->msg,"Hello World");
    pthread_t worker;
    printf("[%s]\n",f->msg);
    // attr initialization is not shown
    pthread_create(&worker,&attr,receive_data,&f);
}

Other initialization code for pthread is not shown.

How can I resolve this problem?

f->msg[0] = '\0'; is completely useless in that code of yours — Vinicius Kamakura
– Vinicius Kamakura, Commented Jun 19, 2011 at 20:52
Yeah, I see that, in the actual code, I do strcat instead of strcpy which needs to locate '\0'. But, it was my mistake in this context. — user482594
– user482594, Commented Jun 19, 2011 at 21:40

Mat · Accepted Answer · 2011-06-19 20:46:48Z

9

You're passing a pointer-to pointer-to mystruct. Don't do that.

pthread_create(&worker, &attr, receive_data, f);

is enough. f is already of type mystruct*. &f is of type mystruct**.

answered Jun 19, 2011 at 20:46

Mat

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R.. GitHub STOP HELPING ICE Over a year ago

Also OP's program almost surely terminates before it has a chance to print anything since it runs off the end of main...

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