你知道如何解决 "error: expected expression const char new_body[] = sprintf(const char *body, "Il valore del sensore è: %.2f", humidity);" 的问题吗？

Question

我有一个问题，发送一个HTTP响应到服务器，我必须使用 "sprintf"

while (1) {


    float temp = sht31.readTemperature();
    float humidity = sht31.readHumidity();


    if(temp!=stored_temp || humidity!=stored_humidity){
        printf("Change detected!\n");
        stored_temp=temp;
        stored_humidity=humidity;

    lcd.locate(3, 3);
    lcd.printf("Temperature: %.2f C", temp);
    lcd.locate(3, 13);
    lcd.printf("Humidity: %.2f %%", humidity);

    {
    HttpRequest* post_req = new HttpRequest(network, HTTP_POST, "http://34.212.30.54:5000/api/transmit_data");
    post_req->set_header("Content-Type", "application/json");

    const char body[ ] = "{\"student_id\": xxxxxxx, \"sensor-type\": humidity, \"data\": 39.93}";

    //float new_data;

这是给我主要问题的关键点，有什么建议吗？

    const char new_body[ ] = sprintf(const char body, "Il valore del sensore è: %.2f", humidity);

    printf("Il valore selezionato dall'utente è:\n%s\n", new_body);

    HttpResponse* post_res = post_req->send(new_body, strlen(new_body));
    if (!post_res) {
        printf("HttpRequest failed (error code %d)\n", post_req->get_error());
        return 1;
    }

    printf("\n----- HTTP POST response -----\n");
    dump_response(post_res);

    delete post_req;
}

Answer 1

Details of sprintf can be found at 
http://www.cplusplus.com/reference/cstdio/sprintf/

int sprintf ( char * str, const char * format, ... );

1. It returns int not const char[].
2. you can do sprintf as:

char body[MAX_PATH];
sprintf(body, "Il valore del sensore è: %.2f", humidity);

Now body has char array to be used in printf and further.

printf("Il valore selezionato dall'utente è:\n%s\n", body);