linux需要itoa函数，下面我就提供一份跨平台的itoa函数。
//return the length of result string. support only 10 radix for easy use and better performance
int my_itoa(int val, char* buf)
{
const int radix = 10;
char* p;
int a; //every digit
int len;
char* b; //start of the digit char
char temp;
p = buf;
if (val < 0)
{
*p++ = '-';
val = 0 - val;
}
b = p;
do
{
a = val % radix;
val /= radix;
*p++ = a + '0';
} while (val > 0);
len = (int)(p - buf);
*p-- = 0;
//swap
do
{
temp = *p;
*p = *b;
*b = temp;
--p;
++b;
} while (b < p);
return len;
}
这个函数会返回字符串的长度，在某些场合下会很有用。
我测试了一下，这个函数大概比MFC自带的itoa要快20%左右。
(因为不需要在循环体内判断if (a > 9)了，所以更快)。
2010/1/8 改进版：
//return the length of result string. support only 10 radix for easy use and better performance
int my_itoa(int val, char* buf)
{
const unsigned int radix = 10;
char* p;
unsigned int a; //every digit
int len;
char* b; //start of the digit char
char temp;
unsigned int u;
p = buf;
if (val < 0)
{
*p++ = '-';
val = 0 - val;
}
u = (unsigned int)val;
b = p;
do
{
a = u % radix;
u /= radix;
*p++ = a + '0';
} while (u > 0);
len = (int)(p - buf);
*p-- = 0;
//swap
do
{
temp = *p;
*p = *b;
*b = temp;
--p;
++b;
} while (b < p);
return len;
}
改进：将除法运算从有符号整数改为了无符号整数。典型速度从240毫秒左右，提高到了180毫秒左右。作为对比，MFC自带的itoa耗时是320毫秒左右。
(x86机器做无符号整数的除法要更快一些，汇编指令不同)
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