Thread: function parameters

It has been a while since I have been working with details on specifically appropriately passing parameters into a function. Basically, I have a snippet of code as shown below:

Code:

#define BUFFER_SIZE 5

void main(){
       unsigned int temp_res;
       char adc[BUFFER_SIZE];

       void usart_str_write(char* string);
       char Usart_write(char data);         // given by built-in library

       /* some register assignment commands that's not relevant to the problem */

    while(1) {
           temp_res = Adc_Read(0);
           n = sprintf(adc, "%u", temp_res);
           if (n < 0 || n >= BUFFER_SIZE)
                break;
           usart_str_write(adc);
    }
}

void usart_str_write(char* string)
{
	while (null character hasn't been reached)
	{
		Usart_write(string);
		string++;
	}
}

I'm not sure if I should have my usart_str_write as "void usart_str_write(char* string)" to pass adc[] by reference or by "void usart_str_write(char string[]". Does anyone have an insight on this?

Main should return int. See FAQ.
Don't put declarations inside your functions; they should go into a header file.
It's up to you, really, how to pass them. If you do char string[], the entire string is duplicated and passed to the function, but if you use (const) char* string, it will pass the address, which is faster (but also allows it to modify your string). In any case, char* and const char* is standard for all (AFAIK) C library functions.

My code runs on microcontrollers, which is correct to use void main(). I don't want to pass char string[] b/c I don't have the luxury of having the duplication take up more memory. If I pass the address, does the function call automatically dereference string to the address of adc[]?

No. If you pass a pointer, you pass a pointer, end of story. You're going to have to derference it yourself.

So are you suggesting I have something like:

Code:

#define BUFFER_SIZE 5

void usart_str_write(char* string);
char Usart_write(char data);         // given by built-in library

void main(){
       unsigned int temp_res;
       char adc[BUFFER_SIZE];
       char* adc_str;

       /* some register assignment commands that's not relevant to the problem */

    while(1) {
           temp_res = Adc_Read(0);
           n = sprintf(adc, "%u", temp_res);
           if (n < 0 || n >= BUFFER_SIZE)
                break;
           adc_str = &adc;
           usart_str_write(adc_str);
    }
}

void usart_str_write(char* string)
{
	while (null character hasn't been reached)
	{
		Usart_write(string);
		string++;
	}
}

Originally Posted by stanlvw

So are you suggesting I have something like:

Code:

#define BUFFER_SIZE 5

void usart_str_write(const char* string);
char Usart_write(char data);         // given by built-in library

void main(){
       unsigned int temp_res;
       char adc[BUFFER_SIZE];
       char* adc_str; /* Remove */

       /* some register assignment commands that's not relevant to the problem */

    while(1) {
           temp_res = Adc_Read(0);
           n = sprintf(adc, "%u", temp_res);
           if (n < 0 || n >= BUFFER_SIZE)
                break;
           adc_str = &adc; /* Remove */
           usart_str_write(adc);
    }
}

void usart_str_write(const char* string)
{
	while (null character hasn't been reached)
	{
		Usart_write(string);
		string++;
	}
}

You don't need an extra var for getting the address.
Further, on (char) arrays, you don't need to do & to get the address. It's done automatically. So just pass adc.
Also add const to your function arguments unless you're going to modify the string (I assume you're not?).

I would not be modifying thstring in usart_str_write. Thanks for the heads up on the const for prevent unintended modifications.

No problem.

I have another problem with the compiler complaining about:

Code:

usart_str_write(adc[]);

I have tried both adc and adc[], but the compiler complained about the same message about it being an illegal expression and implicit cast of integral value to pointer. Any ideas on what's happening that's causing this complaint?

What's the code and what line does the error occour on?

Code:

#define BUFFER_SIZE 5

void usart_str_write(const char* string);
char Usart_write(char data);         // given by built-in library

void main(){
       unsigned int temp_res;
       char adc[BUFFER_SIZE];
       char* adc_str; /* Remove */

       /* some register assignment commands that's not relevant to the problem */

    while(1) {
           temp_res = Adc_Read(0);
           n = sprintf(adc, "%u", temp_res);
           if (n < 0 || n >= BUFFER_SIZE)
                break;
           adc_str = &adc; /* Remove */
           usart_str_write(adc);
    }
}

void usart_str_write(const char* string)
{
	while (null character hasn't been reached)
	{
		Usart_write(string);
		string++;
	}
}

The error is on the line highlighted in red. The message is shown in http://imagebin.ca/view/89NYVWS.html.

I dunno, that should work, as it works for me.
Also,

Code:

Usart_write(string);

...should be...

Code:

Usart_write(*string);

Since it takes a char.

Elysia: It works on the compiler that you're using?

Yes, it does.
It compiles fine on VC++ 2005.