2D global array without knowing lengths. Best practice? - c

Question

I need to have buffers that I will use it in multiple different types of threads. So the array needs to be global.
Buffer size and number of buffers are given as input to the program.
As an alternative I could implement linked list maybe.
What is the best way to implement such buffers? Can you provide a sample?
Any help is appreciated!

Answer 1

I don't understand what do you mean by "without knowing length", if you pass size of each buffer and number of buffers as input parameters then you know every required length.
Maybe this is not the best, but that would be my way.
First declare global buffer and threads.
static void ** buffer;
pthread_t tid[2];
Here is described how the threads will work. First buffer will assign with data first two sub-buffers. Second will do the same with the other two.
void *assignBuffer(void *threadid) {
pthread_t id = pthread_self();
if (pthread_equal(id, tid[0])) {
strcpy(buffer[0], "foo");
strcpy(buffer[1], "bar");
} else {
strcpy(buffer[2], "oof");
strcpy(buffer[3], "rab");
}
return NULL;
}
Converting program args from string to integer.
Here we assign buffer with arrays of unknown type.
Here we assign each buffer with his size in bytes.
Finally we create working threads. The important thing is that they
will run simultaneously.
Waiting until all threads done their job.
Simple print buffer contents.
Ok, here is the code.
int main(int argc, char **argv) {
//1
int bufferSize = atoi(argv[1]);
int buffersAmount = atoi(argv[2]);
//2
buffer = malloc(sizeof(void *)*buffersAmount);
//3
int i;
for (i = 0; i < buffersAmount; ++i) {
buffer[i] = malloc(bufferSize);
}
//4
i = 0;
while (i < 2) {
pthread_create(&tid[i], NULL, &assignBuffer, NULL);
++i;
}
//5
for (i = 0; i < 2; i++)
pthread_join(tid[i], NULL);
//6
for (i = 0; i < 4; ++i) {
printf("%d %s\n", i, (char*)buffer[i]);
}
for (i = 0; i < buffersAmount; ++i) {
free(buffer[i]);
}
return 0;
}
Feel free to ask if you don't understand something, also sorry for my english it is not my native language.