innet_addr函数实现（暂无错误校验），网络字节序固定

#include <stdio.h>
#include "string.h"

unsigned long inet_addr(const char *str)
{
	unsigned long num = 0;
	int i = 1, j = 1;
	const char *pstr[4] = { NULL };
	pstr[0] = strchr(str, ‘.‘);
	pstr[1] = strchr(pstr[0] + 1, ‘.‘);
	pstr[2] = strchr(pstr[1] + 1, ‘.‘);
	pstr[3] = strchr(str, ‘\0‘);

	for (j = 0; j < 4; j++)
	{
		i = 1;
		if (j == 0)
		{
			while (str != pstr[0])
			{
				num += (*--pstr[j] - ‘0‘) * i;
				i *= 10;
			}
		}
		else
		{
			while (*--pstr[j] != ‘.‘)
			{
				num += (*pstr[j] - ‘0‘) * i << 8 * j;
				i *= 10;
			}
		}
	}
	return num;
}

int main()
{
	char str[20] = { ‘\0‘ };
	while (true)
	{
		printf("请输入需要转换的IP地址：");
		scanf_s("%s", str, sizeof(str));
		unsigned long addr = inet_addr(str);
		printf("%s 转换后：0x%x\n", str, addr);
	}
	return 0;
}