#include <stdio.h>
#include <iostream>
int main(){
printf("Hello world! "); // 教科書的寫法
puts("Hello world!"); // 我最喜歡的
puts("Hello" " " "world!"); // 拼接字符串
std::cout << "Hello world!" << std::endl; // C++風格的教科書寫法
return 0;}
2、用宏寫的“Hello world!”
“#”可以“提取”參數的名 字，把它變成字符串。
#include <stdio.h>
#define Say(sth) puts (#sth)
int main(){
return Say(Hello world!);
}
3. 斷章取義的“Hello world!”
#include <stdio.h>
int main(){
return puts ("Do not say: Hello world! "[12]);
}
4. 退出時運行的“Hello world!”
atexit()註冊回調函數。這個函數可以調用多次，最後註冊的函數最先執行。
#include <stdio.h>
#include <stdlib.h>
void say(){printf("world! ");}
void sth(){printf("Hello ");}
int main(){
return atexit(say), atexit (sth);
}
5. 讀取自己的“Hello world!”
// Hello world!
#include <iostream>
#include <fstream>
#include <string>
int main(){
std::ifstream ifs(__FILE__);
std::string say, some, word;
ifs >> say >> some >> word;
std::cout << some << " " << word;
return 0;
}
6. 話分兩頭的“Hello world!”
聲明壹個全局的類的實例，在 main 函數執行之前會調用這個類的構造函數，結束之後則會調用析構函數。
#include <iostream>
class say{
public:say(){std::cout << "Hell";}
~say(){std::cout << "world!";}
}hello;
int main(){
std::cout << "o ";
return 0;
}
7. 傳入模板的“Hello world!”
#include <iostream>
template <char * words>
class say{
public:
void operator () (){std::cout << words;}
};
char hello[] = "Hello world!";
int main(){
return say<hello>()(), 0;
}
8. 調用私有函數的“Hello world!”
#include <iostream>
#include <cstddef>
class secret{
private:
virtual void say(){std::cout << "Hello world!";}
};
int main(){
secret word;
(reinterpret_cast<void (*)()>(**(intptr_t**)(&word)))();
return 0;
}
9. 直接修改函數的返回地址
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
void say(){
puts("Hello world!");
exit(0);
}
int main()
{
volatile intptr_t a = 0;
volatile intptr_t * p = &a;
*(p + 2) = (intptr_t)say;
*(p + 3) = (intptr_t)say;
return 0;
}
10. 外星人說的“Hello world!”
#include <stdio.h>
void alien_say (char * p){
while (putchar (*(p += *(p + 1) - *p)));
}
int main(){
return alien_say ("BETHO! Altec oh liryom(a loadjudas!) dowd."), 0;
}