<cstring> append() 详解及其扩展(int, char):

#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<cstdio>
using namespace std;
int main()
{   cout<<"第三: 字符串的添加与复制 append();\nstring d(a);\ncout<<d<<endl;\n//或者 d=d+a;/nd.append(b);\n";

    cout<<"1.在d的末尾添加字符串a\n\n";
    string d(a);
    d.append(b);
    cout<<d<<endl<<endl;

    cout<<"2.在d的末尾添加字符串/nb(0位置开始,2个长度)的数据\n\n";
    cout<<"d.append(b,0,2);\ncout<<d<<endl;\n";
    d.append(b,0,2);
    cout<<d<<endl<<endl;

    cout<<"3.添加4个 ~ 字符\n\n";
    cout<<"d.append(4,'~');\n";
    cout<<"cout<<d<<endl<<endl;\n";
    d.append(4,'~') ;
    cout<<d<<endl<<endl;

    system("pause");
    system("cls");

    cout<<"4. int 与 char 型添加 (好高兴自己想到的int ^_^ )\n";
    cout<<"char app[100]=\"aaabbb\";";
    cout<<"\nstring charr(\"-_-\");\n";
    cout<<"charr.append(app);\ncout<<charr<<endl\n";
    char app[100]="aaabbb";
    string charr("-_- ");
    charr.append(app);
    cout<<charr<<endl<<endl;

    cout<<"charr.append(app,4);\ncout<<charr<<endl<<endl;\n";
    charr.append(app,4);
    cout<<charr<<endl<<endl;

    cout<<"char型数组全部,char型数组的前4个\n\n****如果要添加中间***\n";
    cout<<"string tmp;\nstring tmp;tmp.assign(app);\ncharr.assign(\"\");\ncharr.append(tmp,1,4);\ncout<<charr<<endl<<endl;\n";
    string tmp;
    tmp.assign(app);
    charr.assign("");
    charr.append(tmp,1,4);
    cout<<charr<<endl<<endl;

    cout<<"5.int  double 等等 通过 sprintf() <cstdio>作为转接\n";
    cout<<"int aaa=15314;\ndouble bbb=3.1415;\nchar aa[10];\nsprintf(aa,\"%d\",aaa);\ncharr.append(aa,0,4);\nsprintf(aa,\"%f\",bbb);\ncharr.append(aa,0,4);\ncout<<charr<<endl;\n";
    int aaa=15314;
    double bbb=3.1415;
    char aa[10];
    sprintf(aa,"%d",aaa);
    charr.append(aa,0,4);
    sprintf(aa,"%f",bbb);
    charr.append(aa,0,4);
    cout<<charr<<endl<<endl;

    system("pause");
    system("cls");
    return 0;
}

<cstring> assign() 、 copy() 详解:

#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<cstdio>
using namespace std;
int main()
{

    cout<<"第二: 字符串的赋值 assign();"<<endl;
    cout<<"1.感觉就像是append不过是抹除-覆盖\n";
    cout<<"string e;\nchar f[10]=\"123456\"\ne.assign(f);\ne+=' ';\ncout<<e<<endl<<endl;\n";
    string e;
    char f[10]="123456";
    e.assign(f);
    e+=' ';
    cout<<e<<endl<<endl;

    cout<<"2.string区间 赋值都类似吧\n";
    cout<<"e.assign(f,3,3);\ne+=' ';\ncout<<e<<endl<<endl;\ne.assign(f,3);\ncout<<e<<endl;\n";
    e.assign(f,3,3);
    e+=' ';
    cout<<e<<endl;
    e.assign(f,3);
    cout<<e<<endl<<endl;

    cout<<"3.某字符串char型 全部\n";
    cout<<"char ssr[10]=\"asdqwezxc\";\ne.assign(ssr);\ncout<<ssr<<endl;\n";
    char ssr[10]="asdqwezxc";
    e.assign(ssr);
    cout<<ssr<<endl<<endl;

    cout<<"4.某字符串char型 前num个\n";
    cout<<"e.assign(ssr,4);\ncout<<e<<endl;\n";
    e.assign(ssr,4);
    cout<<e<<endl<<endl;

    cout<<"5.某字符赋值\n";
    cout<<"赋值3个6\n";
    e.assign(3,'6');
    cout<<e<<endl<<endl;

    cout<<"copy() 将d中的2位置开始的12个字符覆盖到char型数组ss上\n 必须为-> char型 <-否则报错";
    cout<<" char ss[10]=\"123\";\n string dd;\nd.copy(ss,12,2);\ncout<<ss<<endl;\n";
    char ss[15]="123";
    string dd("abcdefghijklmn");
    dd.copy(ss,12,2);
    cout<<ss<<endl<<endl;

    system("pause");
    system("cls");
        return 0;
}

<cstring> 创建详解

#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<cstdio>
using namespace std;
int main()
{

    //1. 字符串的创建
    cout<<"第一:字符串的创建!\n\n";
    string a(4,'a');
    cout<<"1.以 a 为原字符 4单位大小\n\n";
    cout<<"string a(4,'a');\ncout<<a<<endl;\n";
    cout<<a<<endl<<endl;

    cout<<"2.任意大小的字符串\n\n";
    cout<<"string b(\"bbbbbb\");\ncout<<b<<endl;\n";
    string b("bbbbbb");
    cout<<b<<endl<<endl;

    cout<<"3.把某一字符串的某一部分\n(0位置开始4个长度)给c\n\n";
    cout<<"string c(a,0,4) ;\ncout<<c<<endl;\n";
    string c(a,0,4) ;
    cout<<c<<endl<<endl;

    cout<<"4. 10长度原长度不足补*;\n\n";
    cout<<"c.resize(10,'*');\ncout<<c<<endl;\n";
    c.resize(10,'*');
    cout<<c<<endl<<endl;

    system("pause");
    system("cls");
    return 0;
}

Vs2017 使用 strcpy 的时候会报错，提示 strcpy 是不安全的，需要用 strcpy_s 代替。

#include "pch.h"
#include <iostream>
#include <cstring>

using namespace std;

int main()
{
    char str1[11] = "hello";
    char str2[12] = "world";
    char str3[11];
    int len;


    //复制str1到str2
    strcpy_s(str3, str1);
    cout << "strcpy(str3, str1):" << str3 << endl;

    return 0;
}

关于字符数组为什么可以以数组名来用cout输出数组内容，而普通数组不行。

先上范例：

int a[10] = {1,2,3,6,7};
char b[6] = {'h','a','p','p','y','\0'};
char c[] = "happy";
cout<<a<<endl;
cout<<b<<endl;
cout<<c<<endl;

输出结果为:

0x22fe6c
happy
happy

从以上范例可以看出，普通数组中以数组名用cout来输出，只会得到一串地址；用字符数组则会输出数组中的内容。

那为什么会这样呢？

答案：因为 char 型数组中的每一个元素都是一字节，所以每一个字符之间的地址都是 +1 的是连续的，所以当 cout 输出时读到字符数组中的 \0 便停止输出; 而 int 数组每个元素占 4 个字节所以数个数组中每个元素地址的间隔是 4，但其实它也是连续的，出现乱码是因没找到结束符。