在va_arg不遞增C++

Question

我有我的printf（）函數實現即時通訊的OS的錯誤。基本上問題是，它通過列表增加劑量。例如可以說我有：

printf("%d %d",19,58); 

什麼會顯示在我的操作系統是：

19 19 

58由於某些原因不打算thourgh。我已經調試這個相當長的一段時間，但無法找到問題:(這裏是stdio.C++：

#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 

就像我上面描述，它不是：

#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); 
} 

和stdio.h中通過args作爲某種原因遞增幫助將不勝感激:)

Answer 1

通arg到您的putchar功能通過引用而不是按值！

​​

發生了什麼事是，它就會增加你的putchar函數中，但隨後，函數返回，因爲putchar傳遞一個副本，而不是它的一個引用它在printf對變量沒有影響。