Thread: Variable function arguments.

I want to use variable arguments

Code:

void va_test(int num_args, ...)
{
    va_list valist; 
    
    va_start(valist, num_args); 
    
   for (int i = 0; i <= num_args; i++)
       int sum += va_arg(valist, int);
}

But what if the arguments have different types

Code:

va_test(4, 1, "aa" , 2, "bb" );

How can I check the data type?

Code:

void va_test(int num_args, ...)
{
    va_list valist; 
    
    va_start(valist, num_args); 
    
   for (int i = 0; i <= num_args; i++)
  {
       //if arg is int
       int sum = va_arg(valist, int);
       //if arg is string
       char *str = va_arg(valist, char *);
  }
}

You would do something like what the printf family of functions does: have a known parameter that describes the types of the variable arguments. In the case of printf, it is a format string with prescribed format specifiers, but of course you could take your own approach.

This way it works

Code:

void MyPrintf(int argc, ...)
{
    int i;
    int val;
    char *strp;
    VAR var;
    
    va_list valist; 
    
    va_start(valist, argc); 
    
    //first argument is a resulting string
    char *string = va_arg(valist, char *);
   
    for (i = 1; i < argc; i++)
    {
        var = va_arg(valist, VAR);
  
        switch (var.type)
        {
            case VTYPE_BYTE:  
            case VTYPE_SHORT:
            case VTYPE_INT:
              val = (int)var.value;
             break;
            
            case VTYPE_STR:
              strp = (char *)var.value; 
              break;
        }
   
        if (var.type < VTYPE_STR)
        {
            strp = loc_itoa(val);
            strcat(string, strp);
        }
        else
           strcat(string, strp);     
    }
    
   strcat(string, "\0");
   
   va_end(valist); 
}

uint32_t COM_Printf()
{
  char str[128] = { '\0' };
    
    VAR vars[4];
    
    vars[0].type = VTYPE_BYTE;
    vars[0].value = (void *)1;
    vars[1].type = VTYPE_STR;
    vars[1].value = (void *)"aa";
    vars[2].type = VTYPE_INT;
    vars[2].value = (void *)1234;
    vars[3].type = VTYPE_STR;
    vars[3].value = (void *)"bb\r";
    
   MyPrintf(5, str, vars[0], vars[1], vars[2], vars[3]);
   
   USART_SendString(SYS_USART, str);
      
   return MSG_OK;
}