用C动态构造联合

Question

我正在尝试用ESP32动态设置WIFI的配置。

取决于UUID的设备ID，我想设置SSID。

我试着把角色变量。然而，我失败了

 // Original code
   wifi_config_t ap_config =
       {
           .ap = {
               .ssid = 'WIFI_SSID', // I would like to change .ssid as variable
               .ssid_len = strlen(WIFI_AP_SSID),
               .password = WIFI_AP_PASSWORD,
               .channel = WIFI_AP_CHANNEL,
               .ssid_hidden = WIFI_AP_SSID_HIDDEN,
               .authmode = WIFI_AUTH_WPA2_PSK,
               .max_connection = WIFI_AP_MAX_CONNECTIONS,
               .beacon_interval = WIFI_AP_BEACON_INTERVAL,
           },
       };


// For example, I would like to set SSID name by using another variable
char ssid[10] = "anoter_ssid_name";

wifi_config_t ap_config =
       {
           .ap = {
               .ssid = ssid, // I would like to change .ssid as variable
               .ssid_len = strlen(WIFI_AP_SSID),
           },
       };

Answer 1

这绝对是错误的：

.ssid = 'WIFI_SSID', 

下一步:基本上，您不能在静态存储持续时间初始化器中使用not const表达式。你需要在函数中这样做。

wifi_config_t ap_config =
{
    .ap = {
        .ssid = "WIFI_SSID", // I would like to change .ssid as variable
        .ssid_len = sizeof("WIFI_SSID") - 1,
        .password = WIFI_AP_PASSWORD,
        .channel = WIFI_AP_CHANNEL,
        .ssid_hidden = WIFI_AP_SSID_HIDDEN,
        .authmode = WIFI_AUTH_WPA2_PSK,
        .max_connection = WIFI_AP_MAX_CONNECTIONS,
        .beacon_interval = WIFI_AP_BEACON_INTERVAL,
    },
};

wifi_config_t *setSSID(wifi_config_t *cfg, const char *ssid)
{
    strcpy(cfg -> ssid, ssid);
    cfg -> ssid_len = strlen(ssid);
    rerutn cfg;
}

Answer 2

您需要复制ssid字符串，因为struct的ssid字段被声明为uint8_t [10]，因此已经分配了空间。如果将上面的尝试声明为指针，您的尝试就会奏效。

strcpy(ap_config.ap.ssid, ssid);
ap_config.ap.ssid_len = strlen(ssid);

Answer 3

如果您想初始化：

wifi_config_t ap_config =
       {
           .ap = {
               .ssid = { ssid[0], ssid[1], ssid[2], ssid[3], ssid[4], ssid[5], ssid[6], ssid[7], ssid[8], ssid[9] },
               .ssid_len = strlen(WIFI_AP_SSID),
           },
       };

您可以将每个元素初始化封装在针对长度的检查中，以防止溢出：

 .ssid = {
     strlen(ssid) > 0 ? ssid[0] : 0,
     strlen(ssid) > 1 ? ssid[1] : 0,
     strlen(ssid) > 2 ? ssid[2] : 0,
     strlen(ssid) > 3 ? ssid[3] : 0,
     // etc...

但是这样的代码并不是最优的。最简单的听起来像是你真的很想复制：

wifi_config_t ap_config;
strncpy(ap_config.ap.ssid, ssid, sizeof(ap_config.ap.ssid));
ap_config.ap.ssid_len = strlen(ssid);