Custom Arduino library problem

Question

I have made my custom serial(UART) library. So I made uart.h and uart.cpp files as following.

uart.h

#ifndef UART_H
#define UART_H
#include <avr/io.h>
#include <stdlib.h>
//creating class named uart
class uart{
 public:
 // creating constructor
 uart(void);
 //function to start uart at given baudrate
 void start(int baudrate);
 // function to read uart input
 unsigned char read();
 // function to print data on serial monitor
 void print(unsigned char data);
 // function to print string on serial monitor
 void print(char *string);
 // function to print data with given base
 void print(unsigned char data,unsigned int base);
 //function to print data like printf
 void print(char* str,unsigned char data);
 // function to read data by printing string
 unsigned char read(char* string);
};
#endif

uart.cpp

#include "uart.h"
uart::uart(void);
void uart::start(int baudrate){
 long BAUDRATE = ((F_CPU)/(baudrate*16UL)-1);
 UBRR0H = (BAUDRATE >> 8);
 UBRR0L = BAUDRATE;
 // enable recieve and transmit
 UCSR0B |= 1 << RXEN0 | 1 << TXEN0;
 // data size is equal to 8 bits
 UCSR0C |= 1 << UCSZ00 | 1 << UCSZ01;
}
unsigned char uart::read(){
 //wait until receive complete.
 while(!(UCSR0A & (1 << RXC0)));
 // return received byte
 return UDR0;
}
void uart::print(unsigned char data){
 // wait until UDR is empty
 while(!(UCSR0A & (1 << UDRE0)));
 //place data into UDR
 UDR0 = data;
}
void uart::print(unsigned char* string){
 int index = 0;
 // print string character by character
 while(string[index] != '0円'){
 print(string[index]);
 index++;
 }
}
void uart::print(unsigned char data,unsigned int base){
 //buffer to store converted data
 char buffer[10];
 //convert data to ascii
 itoa(data,buffer,base);
 //print converted data
 print(buffer);
}
// function to print data like printf(%d,data);
void uart::print(char* str,unsigned char data){
 int index = 0;
 // print string character by character
 while(str[index] != '0円'){
 if(str[index] == '%'){
 index++;
 if(str[index]=='d') print(data,10);
 else if(str[index] == 'b') print(data,2);
 else if(str[index] == 'x') print(data,16);
 index++;
 }
 print(str[index]);
 index++;
 }
}
unsigned char uart::read(unsigned char* string){
 // print given string
 print(string);
 // return read char
 return(read());
}

test.cpp

#include "uart.h"
int main(){
 uart.start(9600);
 uart.print("Hello world\n");
}

Now all of above function works if i write all function and declations in single .h file and don't divide my header file in .h and .cpp file. if i compile this given program i get following error.

Error

src/uart.cpp
src/uart.cpp:3:16: error: declaration of 'uart::uart()' outside of class is not definition [-fpermissive]
 uart::uart(void);
 ^
src/uart.cpp:39:6: error: prototype for 'void uart::print(unsigned char*)' does not match any in class 'uart'
 void uart::print(unsigned char* string){
 ^
In file included from src/uart.cpp:1:0:
src/uart.h:31:7: error: candidates are: void uart::print(char*, unsigned char)
 void print(char* str,unsigned char data);
 ^
src/uart.h:28:7: error: void uart::print(unsigned char, unsigned int)
 void print(unsigned char data,unsigned int base);
 ^
src/uart.h:25:7: error: void uart::print(char*)
 void print(char *string);
 ^
src/uart.cpp:30:6: error: void uart::print(unsigned char)
 void uart::print(unsigned char data){
 ^
src/uart.cpp:91:15: error: prototype for 'unsigned char uart::read(unsigned char*)' does not match any in class 'uart'
 unsigned char uart::read(unsigned char* string){
 ^
In file included from src/uart.cpp:1:0:
src/uart.h:34:16: error: candidates are: unsigned char uart::read(char*)
 unsigned char read(char* string);
 ^
src/uart.cpp:20:15: error: unsigned char uart::read()
 unsigned char uart::read(){
 ^
.build/uno/Makefile:166: recipe for target '.build/uno/src/uart.o' failed
make: *** [.build/uno/src/uart.o] Error 1
Make failed with code 2

PS: I use inotool to compile and upload my programs to arduino and it works great. So you will find src/ in error.

Please help me. I'm stuck here.

• Anonymous Penguin: You don't even need the constructor in the first place if it does nothing
• Edgar Bonet: Instead of implementing all the variations of print(), you should just subclass Print and only implement size_t write(uint8_t). This way you avoid code duplication, as there are many classes in the Arduino libraries inheriting Print.
• Mohit Tank: I am making these libraries for learning purpose.i have worked with AVR microcontollers but arduino libraries amazed me.i like its code structure its very well managed.but i found one disadvantage is that memory consumption with its libs.any way thanks for suggestion.
• Butzke: If you solved the question, please mark the asnwer that asnwer the question or make your own answer. And edit the topic removing the [SOLVED]

Answer 1

uart::uart(void);

That's a prototype, not a function. It needs a body. Also, using "void" to say "no parameters" is really confusing. Better to leave it out all together.

uart::uart() {
}

---

uart.start(9600);
uart.print("Hello world\n");

uart is a class, not an instance. You should be using uart::start(9600) if you first set your functions to be static, or create an instance from the uart class:

uart myUart;
int main() {
 myUart.begin(9600);
 myUart.print("Hello world\n");
}

---

Watch your random unsigned entries...

uart.h:
unsigned char read(char* string);
uart.c:
unsigned char uart::read(unsigned char* string){

... There may be others too.

• Mohit Tank: Thank you for your reply.i will correct my mistakes as you mentioned.and let me see if it works or not.
• Majenko: It may take a few iterations. Can't see the wood for the trees at the moment ;) Get rid of these errors first and we'll see where we can go from there.
• Mohit Tank: is it mandatory to use constructor in class,in my case uart::uart(){ }.
• Majenko: If you don't specify a constructor a "default" empty constructor will be provided. It's good to be explicit and provide one thought. You could have it all in the header file though for simplicity... uart() {}
• Mohit Tank: thank you so much @Majenko ,now my header file is working.thank you so so so much..i was stuck from past two days on this error