pjsip进行电话呼叫

pjsip是一个开源的SIP协议栈，可以用于实现基于SIP协议的电话呼叫。以下是一个简单的pjsip电话呼叫的示例代码：

#include <pjsua-lib/pjsua.h>

int main() {
  pj_status_t status;
  pj_caching_pool cp;
  pj_pool_t *pool;
  pjsua_config cfg;
  pjsua_logging_config log_cfg;
  pjmedia_transport_config media_cfg;
  pjmedia_transport *media_transport;
  pjsua_acc_id acc_id;
  pjsua_call_id call_id;
  pj_str_t uri = pj_str("sip:username@domain.com");

  // Initialize pjsua
  status = pj_init();
  pj_caching_pool_init(&cp, NULL, 0);
  pool = pj_pool_create(&cp.factory, "pjsua", 4000, 4000, NULL);
  pjsua_config_default(&cfg);
  cfg.cb.on_incoming_call = NULL;
  cfg.cb.on_call_media_state = NULL;
  cfg.cb.on_call_state = NULL;
  cfg.cb.on_reg_state = NULL;
  pjsua_logging_config_default(&log_cfg);
  log_cfg.console_level = 4;
  log_cfg.level = 4;
  status = pjsua_init(&cfg, &log_cfg, NULL);
  pjsua_transport_config cfg_transport;
  pjsua_transport_config_default(&cfg_transport);
  cfg_transport.port = 5060;
  status = pjsua_transport_create(PJSIP_TRANSPORT_UDP, &cfg_transport, NULL);
  pjsua_start();

  // Register with SIP server
  pjsua_acc_config acc_cfg;
  pjsua_acc_config_default(&acc_cfg);
  acc_cfg.id = pj_str("sip:username@domain.com");
  acc_cfg.reg_uri = pj_str("sip:domain.com");
  acc_cfg.cred_count = 1;
  acc_cfg.cred_info[0].realm = pj_str("domain.com");
  acc_cfg.cred_info[0].scheme = pj_str("digest");
  acc_cfg.cred_info[0].username = pj_str("username");
  acc_cfg.cred_info[0].data_type = PJSIP_CRED_DATA_PLAIN_PASSWD;
  acc_cfg.cred_info[0].data = pj_str("password");
  status = pjsua_acc_add(&acc_cfg, PJ_TRUE, &acc_id);

  // Make outgoing call
  pjsua_call_setting call_setting;
  pjsua_call_setting_default(&call_setting);
  status = pjsua_call_make_call(acc_id, &uri, &call_setting, NULL, NULL, &call_id);

  // Destroy pjsua
  pjsua_destroy();
  pj_pool_release(pool);
  pj_caching_pool_destroy(&cp);

  return 0;
}

这段代码首先初始化了pjsua，然后注册到SIP服务器，最后发起一个呼叫。具体的调用过程可以参考pjsip官方文档。