Interview training Hai Tao 56 questions

Question (16): Run the following C ++ code. What is the output?

class A{public:    virtual void Fun(int number = 10)    {        std::cout << "A::Fun with number " << number;    }}; class B: public A{public:    virtual void Fun(int number = 20)    {        std::cout << "B::Fun with number " << number;    }}; int main(){    B b;    A &a = b;    a.Fun();}

Thought; at first glance, we can see that this question is basically, although a is a reference of Class A, it actually refers to Class B. Here a. Fun () is a virtual function that uses the virtual function pointer to find the fun function in the virtual function table.

So output B: Fun with number is okay, but as for the form parameters in the function, I won't be sure.

The analysis in the Haitao log is very thorough, and the output should be 10

Why are you, Tao said, because the default parameter is actually processed during compilation, a A is a class during compilation, but during running, the virtual function dynamically points to the fun function of Class B, however, the value of number is 10.

Therefore

B::Fun with number  10

Run the following C code. What is the output?

char* GetString1(){    char p[] = "Hello World";    return p;} char* GetString2(){    char *p = "Hello World";    return p;}  int _tmain(int argc, _TCHAR* argv[]){    printf("GetString1 returns: %s. \n", GetString1());    printf("GetString2 returns: %s. \n", GetString2());     return 0;}

Array P [] is the local variable of the function. Exit the function space and recycle it immediately.

* P is a String constant stored in the constant data area, which is global.

So getstring1 returns: a string of garbled characters

Getstring2 returns: Hello World

Question (19): The C code is running. What is the output?

int _tmain(int argc, _TCHAR* argv[]){    char str1[] = "hello world";    char str2[] = "hello world";     char* str3 = "hello world";    char* str4 = "hello world";     if(str1 == str2)        printf("str1 and str2 are same.\n");    else        printf("str1 and str2 are not same.\n");     if(str3 == str4)        printf("str3 and str4 are same.\n");    else        printf("str3 and str4 are not same.\n");     return 0;}

Str1 and str2 are arrays to allocate storage space for them. Of course, the addresses are different.

"Hello world" is a String constant and is stored in the constant data area. Of course, * str3 is the same as the address pointed to by * str4. It has only one copy in the memory.