Question about the String object

Projects Programming
1

hi just a quick question, I'm kinda new at this so bare with me:

i built a library and the one of the parameter's is a String. However the compiler treats it like a char, even saying char in the error code. Although its defined as a String, and the rest of the code dealing with the parameter 'name' says String.

These are the errors:

checkname_on_lcd:9: error: invalid conversion from 'const char*' to 'char'
checkname_on_lcd:9: error: initializing argument 1 of 'Alarm::Alarm(char, char, char, int, int, int, int, int, int, int)'

Is it possible to use strings in a class? i know you can in the program itself as it works. I tried that before building the class. Please and thanks for your time and advice. Also if you treat the name string parameter like a char, the program works, as it obvs thinks it is a char. I have uploaded the earliest code revision i have where i noticed the error.
Srry my serial monitor doesnt work so i included the code for my lcd display.

computer specs
windows 7 64 bit updated
using arduino version 1.01

checkname_on_lcd.ino (598 Bytes)

Alarm.cpp (765 Bytes)

Alarm.h (1.41 KB)

2 
Alarm Alarm1("towak", 'crazyrun', 'xxxxville', 0, 1, 10, 1990, 6, 9, 0);

Strings have to be in double quotes. Your second two are in single quotes.

3

You should avoid using the String class as it is incredibly huge and bulky.

You can do everything using char* that you can with String - it just takes a little more thinking about.

4

Nick Gammon: thx, yeah when I realized I had a problem with the string class, I switched the other 2 to chars so i could work with one controlled string variable. This would allow me to see the differences between the char and the string, as i am very new, and this would be my first project.

majenko: thank you, i will look into char* although i am not familiar with it. I was just trying to use the string class because that is what i'm most familiar with. btw can you use the char* to make a large sentence with, cause i will run into that problem for description and location.

Thanks to everyone for all the help and advice

5

can you use the char* to make a large sentence with

You can fill it with as much data as you allow for:

char myString[128]; // Allocate 128 bytes of data for this string

snprintf(myString,127,"I asked the shop keeper for %d apples, but he only gave me %d.",apples,apples-1);

would end up with myString containing "I asked the shop keeper for 5 apples, but he only gave me 4." if apples was equal to 5.

The "k" of "keeper" is myString[17], as it is the 18th character, and C arrays count from 0 not 1.

You can create a pointer to a string with the * operator:

char *myPtr;

myPtr = myString;
myPtr += 17;
Serial.println(*myPtr);

would print 'k' to the serial device. Again, character 18. myPtr points to the first character of the string. Add 17 to it and you now point to (1+17) the 18th character, which is the k of keeper.

There are many things you can do using pointers like this.

A char * string is terminated with character 0 (not the ASCII character "0", but ASCII code 0). Make sure your strings are terminated with that character or you will start getting garbage. Most operations will put that 0 in there for you automatically, but there are a few (such as strncpy) that won't, so you need to be aware of it.

One trick is to split a string into two separate strings by simply creating a pointer to the first character of the second half of the string, and replacing the previous character (or inserting a new one) with character 0 to terminate the first half of the string.