itoa 함수 소스

/**
* Ansi C "itoa" based on Kernighan & Ritchie's "Ansi C":
*/

void strreverse(char* begin, char* end) {
         char aux;
         while(end>begin)
         aux=*end, *end--=*begin, *begin++=aux;
}

void itoa(int value, char* str, int base) {
       static char num[] = "0123456789abcdefghijklmnopqrstuvwxyz";
       char* wstr=str;
       int sign;

       // Validate base
       if (base<2 || base>35){ *wstr='\0'; return; }

       // Take care of sign
       if ((sign=value) < 0) value = -value;

       // Conversion. Number is reversed.
       do *wstr++ = num[value%base]; while(value/=base);
       if(sign<0) *wstr++='-';
       *wstr='\0';

       // Reverse string
       strreverse(str,wstr-1);
}

	
	


/**



 * Ansi C "itoa" based on Kernighan & Ritchie's "Ansi C"



 * with slight modification to optimize for specific architecture:



 */



void strreverse(char* begin, char* end) {



	char aux;



	while(end>begin)



		aux=*end, *end--=*begin, *begin++=aux;



}
	


void itoa(int value, char* str, int base) {



	static char num[] = "0123456789abcdefghijklmnopqrstuvwxyz";



	char* wstr=str;



	int sign;



	div_t res;
	


	// Validate base



	if (base<2 || base>35){ *wstr='\0'; return; }
	



	// Take care of sign



	if ((sign=value) < 0) value = -value;
	


	// Conversion. Number is reversed.



	do {



		res = div(value,base);



		*wstr++ = num[res.rem];



	}while(value=res.quot);
	


	if(sign<0) *wstr++='-';


	*wstr='\0';
	



	// Reverse string



	strreverse(str,wstr-1);



}
	



/**



 * C++ version std::string style "itoa":



 */



std::string itoa(int value, int base) {



	enum { kMaxDigits = 35 };



	std::string buf;



	buf.reserve( kMaxDigits ); // Pre-allocate enough space.
	


	// check that the base if valid



	if (base < 2 || base > 16) return buf;
	



	int quotient = value;






	// Translating number to string with base:



	do {



		buf += "0123456789abcdef"[ std::abs( quotient % base ) ];



		quotient /= base;



	} while ( quotient );
	


	// Append the negative sign for base 10



	if ( value < 0 && base == 10) buf += '-';






	std::reverse( buf.begin(), buf.end() );



	return buf;



}
	
	


/**



 * C++ version char* style "itoa":



 */



char* itoa( int value, char* result, int base ) {



	// check that the base if valid



	if (base < 2 || base > 16) { *result = 0; return result; }
	




	char* out = result;



	int quotient = value;
	




	do {



		*out = "0123456789abcdef"[ std::abs( quotient % base ) ];



		++out;



		quotient /= base;



	} while ( quotient );
	



	// Only apply negative sign for base 10



	if ( value < 0 && base == 10) *out++ = '-';






	std::reverse( result, out );



	*out = 0;



	return result;
	


}

출처 : http://www.jb.man.ac.uk/~slowe/cpp/itoa.html