strcat标准库函数

 #include <iostream>#include <cstring>//标准库函数的头文件using namespace std;int main(){ char str4[] = "Hello world"; char str5[] = "Hello boy";cout<<strlen(str4)<<endl;cout<<strlen(str5)<<endl; cout << strcat(str4,str5) << endl;cout<<strlen(str4)<<endl;return 0;}