looking at the insert query it has %s so does that mean in the call to function sprintf the value of temperature is inserted to INSERT_DATA and then it is fed to the query variable which is the first in call to sprintf ?
thats what I don't get ? I am not cpp programmer I have been programming with python and still thinking like a python programmer , so any help would be greatly appreciated
so does that mean in the call to function sprintf the value of temperature is inserted to INSERT_DATA
Not exactly.
In that example, INSERT_DATA is the format statement. The format statement contains one format specifier, so one additional argument is needed (for a total of three). The format specifier is an s, so the third argument needs to be a string.
temperature is a string, so it is appropriate as the third argument.
What happens, then, is that literal parts of the format statement are copied to the output buffer, until a forma specifier is encountered. That means that "INSERT INTO test_arduino.temps VALUES (" will be copied to query.
Then, the appropriate value is substituted in place of the format specifier - the string temperature is added to the end of query.
Finally, the remaining literal characters, ", NULL)", in the format statement are added to the end of query.
but of temperature to be a string I would have to convert any string or float to a string ? you meant char datatype ?
There is a format specifier for floats (%f), but the Arduino team disabled support for that format specifier. (It can be re-enabled, relatively simply.) So, yes, you need to convert any float to a string using some other means.
You do not need to convert strings to strings. Yes, a string is a NULL terminated array of chars.
PaulS:
I mean that you really, REALLY, need to buy a C programming book, and spend some time reading.
yes thats a thing I am going to do first. I am just restricted by lack of time and living alone doing every thing by myself.
Its just that in my list of priorities I have a huge pile.
Until you get around to buying that book (Kernighan & Ritchie is highly recommended), this may be useful: www.cplusplus.com/doc/tutorial/ntcs/
--Michael
Your code example looks like it was compiled under Visual Studio and that's not going to work too well with the Arduino. First, the statement:
const char INSERT_DATA[] = "INSERT INTO test_arduino.temps VALUES (%s, NULL)";
the const keyword means you cannot change the content of that string at runtime. I doubt that's what you really want. In the example below, if newData[] is what you want to INSERT into the db, this shell test program might help you see how to build the string:
void setup() {
Serial.begin(9600);
Serial.println("Enter input data (20 chars max):");
}
void loop() {
char insertData[100] = "INSERT INTO test_arduino.temps VALUES ('";
char kbInput[21];
int charsRead;
if (Serial.available() > 0) { // Something's in the Serial buffer...
charsRead = Serial.readBytesUntil('\n', kbInput, sizeof(kbInput) - 1); // Leave room for NULL
kbInput[charsRead] = NULL; // Now it's a C string
strcat(insertData, kbInput);
strcat(insertData, "' NULL)");
Serial.println("SQL string: ");
Serial.println(insertData);
Serial.println("\nEnter input data (20 chars max):");
}
}
Obviously, you'll need to modify it, but it gives you a way to build the query string without using sprintf(), which uses more memory than needed. Make sure you have the input termination textbox set to Newline.
