Arduino: String to int gets strange values

Question

I want to convert a String to an int, and all I could find is that you have to convert the String to a char array and then cast this array to an int, but my code produces strange values and I can't figure out what the problem is.

void ledDimm(String command)
{
    // Get the Value xx from string LEDDimm=xx
    String substring = command.substring(8, command.length());

    Serial.println("SubString:");
    Serial.println(substring);
    Serial.println("SubString Length:");
    Serial.println(substring.length());

    // Create a Char Array to Store the Substring for conversion
    char valueArray[substring.length() + 1];

    Serial.println("sizeof ValueArray");
    Serial.println(sizeof(valueArray));

    // Copy the substring into the array
    substring.toCharArray(valueArray, sizeof(valueArray));

    Serial.println("valueArray:");
    Serial.println(valueArray);

    // Convert char array to an int value
    int value = int(valueArray);

    Serial.println("Integer Value:");
    Serial.println(value);

    // Write the Value to the LEDPin
    analogWrite(LEDPin, value);
}

And the serial output looks like this:

Received packet of size 11
From 192.168.1.4, port 58615
Contents:
LEDDimm=100
SubString:
100
SubString Length:
3
sizeof ValueArray
4
valueArray:
100
Integer Value:
2225

I expected to get an int with the value of 100 but the actual int is 2225?! What have I done wrong here?

Answer 1

There is even an (undocumented) toInt() method in the String class:

int myInt = myString.toInt();

Answer 2

The toInt () method is very useful in this aspect, but I found that it is able to convert only strings of length five or less, especially a value less than 65535 as its the maximum value int can take. Over this value, it just gives random numbers (overflowing values). Please be aware of this when you use this method as it killed a lot of my useful time to figure this out. Hope it helps.

Answer 3

You need to use the function int value = atoi(valueArray); where valueArray is a null terminated string.