va_arg not incrementing C++ - c++

Question

I have a bug with my printf() function im implementing for OS. Basically the problem is, it dosent increment through the list. For example lets say i have:
printf("%d %d",19,58);
what will show on my OS is :
19 19
the 58 for some reason is not going thourgh. I have debugged this for quite some time, but cant find problem :( . Here is the stdio.c++:
#include "stdio.h"
static size_t terminal_row = 0;
static size_t terminal_column = 0;
static uint16_t* VideoMemory =((uint16_t*)0xb8000);
static bool continue_ex = false;
SerialPort sp_std_io;
void printf(char *str, ...)
{
va_list arg;
va_start(arg, str);
for(int32_t i=0;str[i]!='\0'; ++i)
{
putchar(str[i],str[i+1],arg);
}
va_end(arg);
}
void strcat(char *destination, const char *source)
{
int x = 0;
while (destination[x] != '\0')
{
x++;
}
for (int i=0; source[i] != '\0'; i++)
{
destination[x++] = source[i];
}
destination[x] = '\0';
}
void put_char_helper_neg(char chr)
{
const size_t index = (terminal_row * VGA_WIDTH + terminal_column);
terminal_column++;
VideoMemory[index]= (VideoMemory[index] & 0xFF00)|chr;
}
void putstring_t(char str)
{
size_t index = (terminal_row * VGA_WIDTH + terminal_column);
terminal_column++;
VideoMemory[index]= (VideoMemory[index] & 0xFF00)|str;
}
void putchar(char str,char next_str, va_list arg)
{
if(!continue_ex)
{
uint32_t ch_per;
char* str_use,str_use_space;
const char per = '%';
if(str == '\b')
{
terminal_column--;
}
const size_t index = (terminal_row * VGA_WIDTH + terminal_column);
char space = ' ';
switch(str)
{
case '\n':
terminal_row++;
terminal_column = 0;
break;
case '\b':
VideoMemory[index]= (VideoMemory[index] & 0xFF00)|space;
break;
case '%':
switch(next_str)
{
case 'd':
ch_per = va_arg(arg,int);
if(ch_per<0)
{
ch_per = -ch_per;
put_char_helper_neg('-');
}
str_use = itoa(ch_per);
terminal_column++;
for(int32_t i=0;str_use[i]!='\0'; ++i)
{
putstring_t(str_use[i]);
}
// sp_std_io.write_number_serial(ch_per);
// sp_std_io.write_string_serial(str_use);
continue_ex = true;
break;
default:
terminal_column++;
VideoMemory[index]= (VideoMemory[index] & 0xFF00)|per;
}
break;
default:
terminal_column++;
VideoMemory[index]= (VideoMemory[index] & 0xFF00)|str;
break;
}
}
else
{
continue_ex = false;
}
}
int32_t strlen(int8_t* str)
{
int32_t l=0;
while(str[l]!='\0')l++;
return l;
}
char *itoa(int val)
{
uint8_t *ptr;
static uint8_t buffer[16];
ptr = buffer + sizeof(buffer);
*--ptr = '\0';
if (val == 0)
{
*--ptr = '0';
}
else while (val != 0)
{
*--ptr = (val % 10) + '0';
val = val / 10;
}
return((char*)ptr);
}
and stdio.h:
#ifndef _STD_LIB_H_
#pragma once
#define _STD_LIB_H_ 1
#include <stddef.h>
#include <stdint.h>
#include <stdarg.h>
#include "math.h"
#include "serial.h"
static const size_t VGA_WIDTH = 80;
static const size_t VGA_HEIGHT = 25;
//static int num_count_viedo_memory = 0;
void printf(char *str,...);
void putchar(char str,char next_str,va_list arg);
int32_t strlen(int8_t *str);
void strcat(char * Dest, char const * Src);
//int8_t* str_cat(int8_t *dest, const int8_t *src);
void reverse(char str[], int32_t length);
char* itoa(int val);
#endif
Like i described above , it is not incrementing through the args for some reason. Help would be appreciated! :)

Answer 1

Pass arg into your putchar function by reference instead of by value:
void putchar(char str,char next_str, va_list& arg)
What's happening is that it gets incremented inside your putchar function, but then the function returns and it has no effect on the variable in printf because putchar is passed a copy rather than a reference to it.