defining char datatype and and using with sprintf

Question

I had following setup earlier:

    String INSERT_SQL = "";
    // inserting to sql database on mysql server
    INSERT_SQL = "";
    INSERT_SQL.concat("INSERT INTO arduinoSensorData.sensorLog (out_temperature, out_humidity, ");
    INSERT_SQL.concat(" drwngRoom_temperature, drwngRoom_humidity, pot1_soilMoisture, pot1_avg_SoilMoisture,");
    INSERT_SQL.concat(" wateringPot1) VALUES ('");
    INSERT_SQL.concat(outdoorTempInC);
    INSERT_SQL.concat("', '");
    INSERT_SQL.concat(outoorHumidity);
    INSERT_SQL.concat("', '");
    INSERT_SQL.concat(indorTempinC);
    INSERT_SQL.concat("', '");
    INSERT_SQL.concat(h);
    INSERT_SQL.concat("', '");
    INSERT_SQL.concat(val);
    INSERT_SQL.concat("', '");
    INSERT_SQL.concat(avgVal);
    INSERT_SQL.concat("', '");
    if (wateringBasedOnAlarm){
      waterMsg = "water based on alarm";

    } else waterMsg = soilMsg;
    INSERT_SQL.concat(waterMsg);
    INSERT_SQL.concat("');");

And later, I was converting it to char like this:

const char *mycharp = INSERT_SQL.c_str();

Which I realised wrong approach as in every iteration of the loop function of arduino MCU this will consume more memory!

So, I decided to change INSERT_SQL to char instead of declaring it as String at first place.

I initialised INSERT_SQL as char like this:

char INSERT_SQL[295];

Because I realised the total length would not be more than 295,

But when compiler reaches the line:

INSERT_SQL = "";

I got an error saying:

incompatible types in assignment of 'const char [1]' to 'char [295]'

So, this is the first thing I need is to fix it and secondly, I think I cannot use concat with char datatype, so in that case how do I populate values to sql query using sprintf?

What is `which I realised wrong as in avery iteration this will consume more memory !` supposed to mean? — SergeyA, Jan 25 '17 at 19:09
I realise you are wrong....Use `string` again. And `reserve` some space for better performance when appending. — Simon Kraemer, Jan 25 '17 at 19:11
Consider using [`std::ostringstream`](http://www.cplusplus.com/reference/sstream/ostringstream/) instead. — Rob K, Jan 25 '17 at 19:25
@RobK will this work https://gist.github.com/cmaglie/5883185 — Ciasto piekarz, Jan 25 '17 at 19:41
Naming variables in all upper case is a really bad practice. Almost every C and C++ programmer on earth will think it's a macro. — Carey Gregory, Jan 25 '17 at 19:53

score 0 · Answer 1 · answered Jan 25 '17 at 19:48

0

Compiler is exactly telling you what's wrong.

char INSERT_SQL[295];
INSERT_SQL = "";

You probably want to do like:

char INSERT_SQL[295];
INSERT_SQL[0] = 0x00;
::strcat(INSERT_SQL, "INSERT INTO....

answered Jan 25 '17 at 19:48

JazzSoft

392
2
11

Using `::strcat(INSERT_SQL, "INSERT INTO....` what namespace `strcat` would it be using? Do I not have to be explicit? – Ciasto piekarz Jan 25 '17 at 19:52
strcat() is a standard C library function defined in string.h. All C functions are in the global name scope. You don't have to add "::" at the beginning, if you don't want. – JazzSoft Jan 25 '17 at 19:56

defining char datatype and and using with sprintf

1 Answers1