How do you convert sections of char array into float?

Question

I've converted a float into an char array that will be sent over to a server. I want to be able to convert the char array, say from buffer[10]... to buffer [20] converted back into a single float. How can i accomplish this? I only know how to convert entire buffer using atoi but since my char buffer will contain other irrelevent data how can i selecetively do this for certain part of my array?

This is how i converted my float into an char array.

  sprintf(game->buffer,"%f",game->man[playerNumber-48].x);

    //printf("%s\n", game->buffer);

    for(int i = 0; i<11;i++)
    {
        game->send_key_to_server[i+8] = game->buffer[i];
    }

    sprintf(game->buffer,"%f",game->man[playerNumber-48].y);

    for(int i = 0; i<11;i++)
    {
        game->send_key_to_server[i+19] = game->buffer[i];
    }

Basically im sending my players x and y cordinates over to the server as chars.

"converted a float into an char array" - how? more than one way to do it — Joni, May 24 '17 at 07:42
need to see not only what you tried but how you got from float to this array, as that will determine how you get back. — old_timer, May 24 '17 at 07:43
so you want to use sprintf to go from float to ascii then use scanf to go from ascii to float. — old_timer, May 24 '17 at 07:52
you do understand the accuracy you are throwing away by doing that? — old_timer, May 24 '17 at 07:53
I dont want to convert the whole array though since i added other data. If i am not mistaken it will try to convert my whole array? — xxFlashxx, May 24 '17 at 07:54
old_timer thanks. Actually not really, my biggest concern right now is to have the server to sync my player x and y cordinates. This is my first time trying to build a simple game. However, if you have a more accurate way to send the data i'm happy to listen :D — xxFlashxx, May 24 '17 at 07:57

score 2 · Answer 1 · answered May 24 '17 at 08:10

Reading the comments, what you probably want to do is to serialize and de-serialize the data, so that it can be sent as raw data over some form of communication media.

For that purpose, it does not make sense any sense to convert to ASCII. Instead, you'll want a raw data format, which is most compact. This is possible if both computers have the same floating point format and the same endianess. If so, you can simply do:

memcpy(buf, &my_float, sizeof(float)); // transmitter side
memcpy(&my_float, buf, sizeof(float)); // receiver side

where "buf" is whatever data buffer you use to send/receive data through.

chux - Reinstate Monica · Accepted Answer · 2017-05-25T03:35:22.360

To convert a string to a float, atof(), or better, strtod() is sufficient.

To convert a float to a string, code needs to insure enough precision is used and a large enough buffer to save and distinguish all float - about 17 char. Best to use some exponential format like "%e" or "%a".

//                    -  dig  .     digs               e   -  expo \0
#define FLT_STR_SIZE (1 + 1 + 1 + (FLT_DECIMAL_DIG-1) + 1 + 1 + 3 + 1)
char s[FLT_STR_SIZE];
sprintf(s, "%.*e", FLT_DECIMAL_DIG-1, some_float);

Details

How do you convert sections of char array into float?

2 Answers2