atoi()和itoa()的实现

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引子

自己实现一下atoi()和itoa() 这2个函数

实现

my_itoa.cpp

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
using namespace std;
char *  my_itoa( int value, char * str, int base ){
	char array[]={'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
	bool is_minus = false;
	if(value<0){
		is_minus = true;
		value = - value;
	}
	//buffer
	char buffer[256];
	int i=0,j=0;
	int temp;
	while(value){
		temp =value%base;
		buffer[i++]=array[temp];
		value = value/base;
	}
	//cout<<buffer<<endl;
	if(is_minus){
		str[j++] = '-';
	}
	while(--i>=0){
		str[j++]=buffer[i];
	}
	str[j]='\0';
	return str;
}

int main ()
{
  int i;
  char buffer [33];
  printf ("Enter a number: ");
  scanf ("%d",&i);
  itoa (i,buffer,10);
  printf ("decimal: %s\n",buffer);
  my_itoa (i,buffer,10);
  printf ("decimal: %s\n",buffer);
  itoa (i,buffer,16);
  printf ("hexadecimal: %s\n",buffer);
  my_itoa (i,buffer,16);
  printf ("hexadecimal: %s\n",buffer);
  itoa (i,buffer,2);
  printf ("binary: %s\n",buffer);
  my_itoa (i,buffer,2);
  printf ("binary: %s\n",buffer);
  return 0;
}

my_atoi.cpp

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
using namespace std;
bool is_whitespace(char ch){
	if(ch == ' '||ch == '\t'){
		return true;
	}else{
		return false;
	}
}
int my_atoi ( const char * str ){
	// 1.jump over the whitespace character
	const char* p = str;
	while(is_whitespace(*p)){
		p++;
	}
	
	// 2. check plus or minus sign
	int sign = 1;
	if(*p=='-'){
		sign = -1;
		p++;
	}else if(*p=='+'){
		sign = 1;
		p++;
	}
	// 3.deal the number and ignore the other character
	int res = 0;
	while(*p){
		if(*p>='0'&&*p<='9'){
			res = res*10 + (*p - '0');	
		}
		p++;
	}

    return res*sign;
}
int main ()
{
  int i;
  char szInput [256];
  printf ("Enter a number: ");
  fgets ( szInput, 256, stdin );
  i = my_atoi(szInput);
  printf ("The value entered is %d. The double is %d.\n",i,i*2);
  return 0;
}

参考资料

1. atoi
2. itoa

PS

2012年写的文章

请我喝瓶饮料