5.string中几个重要的内容

5.1.C风格字符串的几个函数原型strlen,strcomp,strcat,strcpy,memcpy

 1 #include "pch.h"
 2 #include <iostream>
 3 #include<cstring>
 4 #include<string>
 5 #include<cassert>
 6 using namespace std;
 7 //strlen
 8 size_t str_len(const char *ptr) {
 9     assert(ptr != NULL);
10     size_t cnt = 0;
11     while (*ptr++ != '\0')
12         cnt++;
13     return cnt;
14 }
15 //strcomp
16 int str_comp(const char *ptr_1, const char * ptr_2) {
17     assert(ptr_1 != NULL && ptr_2 != NULL);
18     while (*ptr_1 == *ptr_2) {
19         if (*ptr_1 == '\0')
20             return 0;
21         ++ptr_1;
22         ++ptr_2;
23     }
24     return *ptr_1 - *ptr_2;
25 }
26 //strcat
27 //切记，使用str_cat的时候一定要让第一个传进来的字符串数组有足够大的空间，否则会出错！
28 char * str_cat(char * ptr_3, const char * ptr_4) {
29     char *temp = ptr_3;
30     assert((ptr_3 != NULL) && (ptr_4 != NULL));
31     while (*ptr_3 != '\0') {
32         ptr_3++;
33     }
34     while ((*ptr_3++ = *ptr_4++) != '\0');
35         
36     return temp;
37 }
38 //strcpy
39 //两个字符组数复制的时候应该具有同样的大小！
40 char * str_cpy(char * ptr_5, const char * ptr_6) {
41     assert((ptr_5 != NULL) && (ptr_6 != NULL));
42     while ((*ptr_5++ = *ptr_6++) != '\0');
43     return ptr_5;
44 }
45 
46 int main() {
47     char t[4];
48     char p[50] = { 'a','b','c','\0' };
49     char p_1[] = { 'a','b','c','\0' };
50     char p_2[] = { 'a','b','c','d','\0' };
51     char p_3[] = { 'b','b','c','\0' };
52     cout << "p's length is:" << str_len(p) << endl;
53     if (str_comp(p_1, p_2) < 0)
54         cout << "p_2>p_1" << endl;
55     if (str_comp(p_1, p_3) < 0)
56         cout << "p_3>p_1" << endl;
57     if (str_comp(p, p_1) == 0)
58         cout << "p=p_1" << endl;
59     char *temp = str_cat(p,p_1);
60     while (*temp!='\0')
61     {
62         cout << *temp++;
63     }
64     cout << endl;
65     str_cpy(t, p_1);
66     for (auto x : t) {
67         cout << x;
68     }
69 }