c++第十九天

p109~p110：

 C风格字符串

特点：

1、不方便，不安全，尽量不使用。

2、必须以 ''结束。（只有这样才能使用C风格字符串函数）

3、一般利用指针操作这些字符。

4、可以用字符串字面值来初始化字符数组。

const char ca1[] = "A C-style character string";    // ca1其实是指向数组首元素的指针。

练习 3.37

这道题输出有点奇怪。。。

#include<iostream>
using std::cout;
using std::cin;
using std::endl;
int main()
{
    const char ca[] = {'h', 'e', 'l', 'l', 'o'};
    const char *cp = ca;
    while (*cp) {
        cout << *cp << endl;
        ++cp;
    }
    return 0;
}

输出结果：

D:labs>a
h
e
l
l
o


a

练习 3.38

搬运。

Pointer addition is forbidden in C++, you can only subtract two pointers.

The reason for this is that subtracting two pointers gives a logically explainable result - the offset in memory between two pointers. Similarly, you can subtract or add an integral number to/from a pointer, which means "move the pointer up or down". Adding a pointer to a pointer is something which is hard to explain. What would the resulting pointner represent?

If by any chance you explicitly need a pointer to a place in memory whose address is the sum of some other two addresses, you can cast the two pointers to int, add ints, and cast back to a pointer. Remember though, that this solution needs huge care about the pointer arithmetic and is something you really should never do.

练习 3.39

1

#include<iostream>
using std::cout;
using std::cin;
using std::endl;
#include<cstring>
int main()
{
    const char ca1[] = "string-A";
    const char ca2[] = "string-B";
    if (strcmp(ca1 , ca2) > 0) {
        cout << "string-A big" << endl;
    } else {
        cout << "string-B big" << endl;
    }
    return 0;
}

 2

#include<iostream>
using std::cout;
using std::cin;
using std::endl;
#include<string>
using std::string;
int main()
{
    string s1 = "string-A";
    string s2 = "string-B";
    cout << "Big one is: ";
    if (s1 > s2) {
        cout << s1 << endl;
    } else {
        cout << s2 << endl;
    }
    return 0;
}

 练习 3.40

#include<cstring>
#include<iostream>
using std::cout;
using std::cin;
using std::endl;
int main()
{
    char s1[100] = "stringA";
    char s2[] = "stringB";
    strcat(s1 , s2);
    char s[100];
    strcpy(s , s1);
    cout << s << endl;
    return 0;
}