验证IP地址的程序

编写程序以验证IPv4地址。
根据Wikipedia，IPv4地址以点十进制表示法规范表示，该点由十进制数字组成，每个十进制数字的范围从0到255，由点分隔，例如172.16.254.1

以下是检查给定字符串是否为有效IPv4地址的步骤：

步骤1)用“。”解析字符串作为使用“ strtok()”函数的分隔符。

e.g.ptr = strtok(str, DELIM);

第2步)
A)如果ptr包含任何非数字字符，则返回0
B)将“ ptr”转换为十进制数字，例如“ NUM”
C)如果NUM不在0-255范围内，则返回0
D)如果NUM在0-255的范围内，并且ptr为非NULL，则将“ dot_counter”增加1
E)如果ptr为NULL则转到第3步，否则转到第1步
步骤3)如果dot_counter！= 3返回0否则返回1

C++

// Program to check if a given
// string is valid IPv4 address or not
#include 
using namespace std;
#define DELIM "."
 
/* function to check whether the
   string passed is valid or not */
bool valid_part(char* s)
{
    int n = strlen(s);
     
    // if length of passed string is
    // more than 3 then it is not valid
    if (n > 3)
        return false;
     
    // check if the string only contains digits
    // if not then return false
    for (int i = 0; i < n; i++)
        if ((s[i] >= '0' && s[i] <= '9') == false)
            return false;
    string str(s);
     
    // if the string is "00" or "001" or
    // "05" etc then it is not valid
    if (str.find('0') == 0 && n > 1)
        return false;
    stringstream geek(str);
    int x;
    geek >> x;
     
    // the string is valid if the number
    // generated is between 0 to 255
    return (x >= 0 && x <= 255);
}
 
/* return 1 if IP string is
valid, else return 0 */
int is_valid_ip(char* ip_str)
{
    // if empty string then return false
    if (ip_str == NULL)
        return 0;
    int i, num, dots = 0;
    int len = strlen(ip_str);
    int count = 0;
     
    // the number dots in the original
    // string should be 3
    // for it to be valid
    for (int i = 0; i < len; i++)
        if (ip_str[i] == '.')
            count++;
    if (count != 3)
        return false;
     
    // See following link for strtok()
   
    char *ptr = strtok(ip_str, DELIM);
    if (ptr == NULL)
        return 0;
 
    while (ptr) {
 
        /* after parsing string, it must be valid */
        if (valid_part(ptr))
        {
            /* parse remaining string */
            ptr = strtok(NULL, ".");
            if (ptr != NULL)
                ++dots;
        }
        else
            return 0;
    }
 
    /* valid IP string must contain 3 dots */
    // this is for the cases such as 1...1 where
    // originally the no. of dots is three but
    // after iteration of the string we find
    // it is not valid
    if (dots != 3)
        return 0;
    return 1;
}
 
// Driver code
int main()
{
    char ip1[] = "128.0.0.1";
    char ip2[] = "125.16.100.1";
    char ip3[] = "125.512.100.1";
    char ip4[] = "125.512.100.abc";
    is_valid_ip(ip1) ? cout<<"Valid\n" : cout<<"Not valid\n";
    is_valid_ip(ip2) ? cout<<"Valid\n" : cout<<"Not valid\n";
    is_valid_ip(ip3) ? cout<<"Valid\n" : cout<<"Not valid\n";
    is_valid_ip(ip4) ? cout<<"Valid\n" : cout<<"Not valid\n";
    return 0;
}

输出

Valid
Valid
Not valid
Not valid

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