C语言实现itoa函数

/* A C++ program to implement itoa() */
#include  
using namespace std; 
  
/* A utility function to reverse a string  */
void reverse(char str[], int length) 
{ 
    int start = 0; 
    int end = length -1; 
    while (start < end) 
    { 
        swap(*(str+start), *(str+end)); 
        start++; 
        end--; 
    } 
} 

// Implementation of itoa() 
char* itoa(int num, char* str, int base) 
{ 
    int i = 0; 
    bool isNegative = false; 
  
    /* Handle 0 explicitely, otherwise empty string is printed for 0 */
    if (num == 0) 
    { 
        str[i++] = '0'; 
        str[i] = '\0'; 
        return str; 
    } 
  
    // In standard itoa(), negative numbers are handled only with  
    // base 10. Otherwise numbers are considered unsigned. 
    if (num < 0 && base == 10) 
    { 
        isNegative = true; 
        num = -num; 
    } 
  
    // Process individual digits 
    while (num != 0) 
    { 
        int rem = num % base; 
        str[i++] = (rem > 9)? (rem-10) + 'a' : rem + '0'; 
        num = num/base; 
    } 
  
    // If number is negative, append '-' 
    if (isNegative) 
        str[i++] = '-'; 
  
    str[i] = '\0'; // Append string terminator 
  
    // Reverse the string 
    reverse(str, i); 
  
    return str; 
} 
  
// Driver program to test implementation of itoa() 
int main() 
{ 
    char str[100]; 
    cout << "Base:10 " << itoa(1567, str, 10) << endl; 
    cout << "Base:10 " << itoa(-1567, str, 10) << endl; 
    cout << "Base:2 " << itoa(1567, str, 2) << endl; 
    cout << "Base:8 " << itoa(1567, str, 8) << endl; 
    cout << "Base:16 " << itoa(1567, str, 16) << endl; 
    return 0; 
} 

char* itoa(int value, char* result, int base) {
		// check that the base if valid
		if (base < 2 || base > 36) { *result = '\0'; return result; }

		char* ptr = result, *ptr1 = result, tmp_char;
		int tmp_value;

		do {
			tmp_value = value;
			value /= base;
			*ptr++ = "zyxwvutsrqponmlkjihgfedcba9876543210123456789abcdefghijklmnopqrstuvwxyz" [35 + (tmp_value - value * base)];
		} while ( value );

		// Apply negative sign
		if (tmp_value < 0) *ptr++ = '-';
		*ptr-- = '\0';
		while(ptr1 < ptr) {
			tmp_char = *ptr;
			*ptr--= *ptr1;
			*ptr1++ = tmp_char;
		}
		return result;
	}

引用地址
http://www.strudel.org.uk/itoa/