Passing a variable in string in Embedded C

Question

I am using ATmega8 and I am trying to send string over USART (in printf style) which include a variable .I am using Atmel Studio 6.2 as IDE for AVR programming. Here is my code:-

#define F_CPU 8000000UL
#include <avr/io.h>
#include <util/delay.h>

void USARTInit(uint16_t ubrr_value)  // initialize USART
{

    UBRRL = ubrr_value;
    UBRRH = (ubrr_value>>8);
    UCSRC|=(1<<URSEL)|(1<<UCSZ1)|(1<<UCSZ0);
    UCSRB=(1<<RXCIE)|(1<<RXEN)|(1<<TXEN);

}

void USARTWriteChar(char data) // send character using USART
{

    while(!(UCSRA & (1<<UDRE)));
    UDR=data;
}

void send_string(char s[])   // send string using USART
{
    int i =0;

    while (s[i] != 0x00)
    {
        USARTWriteChar(s[i]);
        i++;
    }
    USARTWriteChar('\n');
}


int main(void)
{
    USARTInit(51);
    char val='A';
    while(1)
    {
        send_string("Value = %c",val);

    }
}

Now when I compile my code I got this error:-

too many arguments to function 'send_string`

So, clearly it is not accepting %c as it does in C programming. Is there a way in embedded C to pass a variable in a string?

Answer 1

too many arguments to function send_string

The message is quite clear there, your send_string() accepts only a pointer to char as input argument, but while calling, you're trying to pass two input arguments "Value = %c",val causing the mis-match.

You cannot use format specifiers here the way you have shown.

In general, the way to go is to use a temporary buffer, use snprintf() to generate the input string and then, pass the buffer to the send_string() call.

That said, since you're only interested in passing the value of c to send_string(), you can reduce the function to take only a char, like

void send_string(char s) { ...

and then, pass the constant (pre-defined) string Value = and then, the input argument go get the same effect.