passing char and float value to a string

Question

I need to send a get request using a string, and so I need to pass a float and a char value to the string in order to send it.Im trying to connect a PIC18F4550 to wifi using a ESP8266 module I also need to read and write into a database. I have been using this function I made to send AT Commands and its been working fine :

void send (char dato[]){
    int i = 0;
    while (dato[i]!=0){
        TXREG=dato[i];
        i++;
        while(TRMT==0);
    }
    TXREG = 0x0D; 
    while(TRMT==0);
    TXREG = 0x0A;
}

The problem I have is that i need to send :

send("GET /ESPic/index3.php?temp=temp&luz=luz");

But luz is char and temp is float.Using a FTDI232 and Arduino IDE I am reading the data between the PIC and the ESP8266.I dont really know how to do what I need.

Please indent your code correctly. Where is `luz` and `temp` in your code? — Jabberwocky, Oct 02 '18 at 15:41
Can you build the message string with `sprintf` before transmitting it? Aside, the code is missing an initial or final status check. — Weather Vane, Oct 02 '18 at 15:43
Note that you might have to enable the `printf` function family in the cross-compiler. Also please see [Using floats with sprintf() in embedded C](https://stackoverflow.com/questions/905928/using-floats-with-sprintf-in-embedded-c). — Weather Vane, Oct 02 '18 at 16:18

score 3 · Answer 1 · edited Oct 02 '18 at 17:52

3

Assumimg your platform supports sprintf, you probably want this:

float temp;
char luz;
...
char buffer[200];
sprintf(buffer, "GET /ESPic/index3.php?temp=%f&luz=%c", temp, luz);
send(buffer);

edited Oct 02 '18 at 17:52

alk

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answered Oct 02 '18 at 16:06

Jabberwocky

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If temp has a 37.5 value and luz a 0 value, what would be the buffer´s length? I need it for the `send("AT+CIPSEND=AA")` in which AA is the length – Sebastián Mayorga Oct 02 '18 at 19:17
Use strlen(buffer) to get the length of the buffer. In your CIPSEND=AA, is AA always 2 characters with leading zero if necessary? Note that leading zero in C means octal. – cup Oct 02 '18 at 20:37
The buffer will be NUL terminated. Read the chapter dealing with strings in your C text book. – Jabberwocky Oct 02 '18 at 20:48

score 1 · Accepted Answer · answered Oct 02 '18 at 17:53

Convert the float to a string first.

When sending a textual version of float, best to use avoid "%f" and use "%e", "%g", or "%a" with enough precision.

"%f" can be very long for large numbers. It coverts to an uninformative +/- "0.000000" for about half of all float (the small ones).

These 3 formats e,g,a have better control on the maximum length and easier to insure the needed precision is used.

float temp;
char luz;
// send("GET /ESPic/index3.php?temp=temp&luz=luz");

#define SEND_FC_FMT "GET /ESPic/index3.php?temp=%.*e&luz=%c"
//                     -   d   .    ddd...ddd            e   - d...d \0 
#define FLT_ESTR_SIZE (1 + 1 + 1 + (FLT_DECIMAL_DIG-1) + 1 + 1 + 5 + 1)
char buffer[sizeof SEND_FC_FMT + FLT_ESTR_SIZE];

sprintf(buffer, SEND_FC_FMT, FLT_DECIMAL_DIG-1, temp, luz);
send (buffer);

passing char and float value to a string

2 Answers2