Sorry for the stupid question, but i'm just looking for another set of eyes, perhaps someone can tell me how can i get this going...

String mystring="";
void setup()
{
Serial.begin(9600);
}

void loop()
{
mystring="The ADC value is: " + analogRead(A15);
Serial.println(mystring);
sendlog(mystring);
delay(10000);
}

void sendlog(const char* message)
{
//do whatever to send this to logging SD...
}

while compiling, i get the following: 

error: cannot convert 'String' to 'const char*' for argument '1' to 'void sendlog(const char*)'

I understand, this is an expected error, but how to i fix this? i want to get away from using String object altogether. The sendlog is a part of other library, which i do not want to modify, but looking to fix my code instead... Anyone has any idea? I tried all different option starting from .toCharArray and ending with strcpy and alike to fix this, but it seems, that nothing is being passed to the sendlog in the end. so, i need to append a string of characters with int, and send it to the sendlog as a char*. This must be very simple, and this is one of those, where i do not seem so see a very obvious solution... Help anyone?

--Andy

Views: 1467

Reply to This

Replies to This Discussion

First, if you try to append a non-string value to a string it'll get weird.  Instead of

mystring="The ADC value is: " + analogRead(A15);

you should use

mystring="The ADC value is: " + String(analogRead(A15), DEC);

to append a new String (created from a decimal value) to your existing String.  Note that the original method won't cause a compile error, but what you get over the serial port will likely be garbage.  (What you're doing is adding the value read from the analog port to the memory location of mystring, and it'll pass that to println which will read from that incorrect point until it encounters a null byte.)

Second, you have to break the String object back to an array of chars, and to do that you have to have an array of chars to put it in.  If you know what the length of your string is going to be, or at least some sort of maximum range, it's pretty easy.  We know that your string will only be 23 characters long ("The ADC value is: " = 18, "1023" [the max analogRead() value] = 4, and one extra for the terminating null character), so our array only has to be that big.  If you change the wording you'll have to resize the array.

char otherString[23]; //char array to copy the String into

mystring.toCharArray(otherstring, mystring.length() + 1); //Copy the string (+1 is to hold the terminating null char)

sendlog(otherString); //send our char array copy of the String object to sendlog()

Char arrays don't offer all the flexibility that a String object does, and they're sometimes kind of hard to work with, but they're a lot smaller and faster (they only take up as much space as there are characters).

I hope this helps you out.  You could achieve the same outcome using only a char array, but the String object is so much easier to use, especially for converting a number to a string and appending one string to another.

I keep reading in the Arduino reference that you can use "Constant String" + analogRead(), myString += 123, and similar constructions, but whenever I do I get random-length garbage.  Using the String constructor to concatenate a number to a string works though.  Who knows.

RSS

Latest Activity

GarageLab posted blog posts
15 hours ago
GarageLab posted a blog post

Scientists Create a Real Hoverboard

Ever since the fictional hoverboards in 1989’s Back to the Future Part II children (and adults)…See More
Wednesday
Colin Goldberg posted a discussion

Can I use my Samsung Tab 4 tablet as a usb host to a beaglebone board black?

Hi,As a newbie to this space, I would like to know what to think about before I try to connect my…See More
Tuesday
Antonio Turner posted a status
Tuesday
GarageLab posted blog posts
Tuesday
Profile IconGeorge Ray Learmond, Steve Barnes and Diego Leite Mendes joined GarageLab (arduino, electronics, robotics, hacking)
Monday
GarageLab posted a blog post
Oct 17
Stu porley is now a member of GarageLab (arduino, electronics, robotics, hacking)
Oct 16
GarageLab posted blog posts
Oct 16
Atari Punk Console posted a status
"I backed Garag Lab Kick Starter Project the Garagino, I can't wait till I get my Garagino! https://www.kickstarter.com/projects/931487098/g"
Oct 15
Profile IconDan bgarage and Joe Cannella joined GarageLab (arduino, electronics, robotics, hacking)
Oct 15
GarageLab posted blog posts
Oct 14
Profile IconSim Wilkins G. Entendez, Charles Hamilton and Colin Goldberg joined GarageLab (arduino, electronics, robotics, hacking)
Oct 13
GarageLab posted a blog post

Flexible 'Tentacle Robots' Could Aid Planetary Exploration

 Researchers are developing new types of robotic systems inspired by elephant trunks, octopus arms…See More
Oct 10
David Rios is now a member of GarageLab (arduino, electronics, robotics, hacking)
Oct 10
GarageLab posted blog posts
Oct 9
Marcelo Rodrigues is now friends with Tharaka Madhusanka and Guruprasad Balaji
Oct 7
GarageLab posted a blog post
Oct 7
GarageLab posted a blog post
Oct 6
Profile IconScorpio Imran, Joaquim Moroni da Silva, Delan and 1 more joined GarageLab (arduino, electronics, robotics, hacking)
Oct 6

© 2014   Created by Marcelo Rodrigues.

Badges  |  Report an Issue  |  Terms of Service