A pretty minimal publisher example using nats.c

publisher.c

#include <nats/nats.h>
#include <string.h>

const char *subj = "foo";
const char *payload = "example";

int64_t start = 0;
int64_t total = 1000000;

volatile int64_t count = 0;
volatile int64_t elapsed = 0;

static void printPerf(const char *label) {
    if (start && !elapsed)
        elapsed = nats_Now() - start;

    if (elapsed <= 0)
        printf("\nNot enough messages or too fast to report performance!\n");
    else
        printf("\n%s %" PRId64 " messages in %" PRId64 " ms (%d msgs/sec)\n",
               label, count, elapsed, (int)((count * 1000) / elapsed));
}

int main(void) {
    natsConnection *conn = NULL;
    natsStatus s = natsConnection_Connect(&conn, NULL);

    if (s != NATS_OK) {
        printf("Error: %u - %s\n", s, natsStatus_GetText(s));
        nats_PrintLastErrorStack(stderr);
        nats_Close();

        return 1;
    }

    printf("Sending %" PRId64 " messages to subject '%s'\n", total, subj);

    start = nats_Now();

    int dataLen = (int)strlen(payload);

    for (count = 0; count < total && s == NATS_OK; count++)
        s = natsConnection_Publish(conn, subj, payload, dataLen);

    if (s == NATS_OK)
        s = natsConnection_FlushTimeout(conn, 1000);

    if (s == NATS_OK)
        printPerf("Sent");
    else
        printf("Error: %u - %s\n", s, natsStatus_GetText(s));

    natsConnection_Destroy(conn);
    nats_Close();

    return 0;
}

#include <nats/nats.h>
#include <stdio.h>
#include <inttypes.h>

int main(void) {
    const char *subj = "foo";
    int64_t total = 1000000, count, start, elapsed;
    char payload[64];
    natsConnection *conn = NULL;
    natsStatus s = natsConnection_Connect(&conn, NULL);

    if (s != NATS_OK) { 
        fprintf(stderr, "Error: %u - %s\n", s, natsStatus_GetText(s)); 
        nats_PrintLastErrorStack(stderr); 
        nats_Close(); 
        return 1; 
    }

    printf("Sending %" PRId64 " messages to '%s'\n", total, subj);
    start = nats_Now();

    // Publish all messages without blocking
    for (count = 0; count < total && s == NATS_OK; count++) {
        int len = sprintf(payload, "example %" PRId64, count);
        s = natsConnection_Publish(conn, subj, payload, len);
    }

    // Flush once at the end to block until all messages reach the server
    if (s == NATS_OK) s = natsConnection_Flush(conn);

    elapsed = nats_Now() - start;
    if (s == NATS_OK && elapsed > 0)
        printf("\nSent %" PRId64 " messages in %" PRId64 " ms (%d msgs/sec)\n",
               count, elapsed, (int)((count * 1000)/elapsed));
    else
        fprintf(stderr, "Error or too fast to measure\n");

    natsConnection_Destroy(conn);
    nats_Close();
    return 0;
}