Cpp Chapter 8: Adventures in Functions Part1

//第一次在博客上发自己的C++ primer plus学习笔记，从现在进度（第8章）开始,用英文也当是练练英语写作了

1. Inline Functions

) When calling a regular function, the program execution will be transfered to the called function and back, thus making it time-consuming under circumstances that call the same short function for a multiple of times. In an inline function, the compiler replaces the function call with corresponding function code, so the program execution don't need to be transfered.

) If the function code's execution time is short relatively to the execution-transfer process, using inline function will save a great proportion of time.

) To implement this feature, common practice is to omit the function prototype and put the entire definition at the beginning of the file with keyword inline.

for example:

 

// example of inline function comparison
#include <iostream>
using namespace std;
double square(double);

int main（）
{
...
}

double sqaure(double x)
{
    return x * x;
}

 

this code uses a function called square. It has only one line of code, so transfer it to inline function:

// example of inline function comparison
#include <iostream>
using namespace std;
inline double square(double x) {return x * x;}

int main()
{
...
}

By adding the inline keyword, you mean that square() is an inline function.

) Back in C, it used #define methods to cope with similar problems. But #define is simply a text substitution, inline functions can pass arguments by value just like normal functions do.

2. Reference Variables

) A reference is a name that acts as an alternative name for a previously defined variable. The main use is as a formal argument to a function so the function could work with the original data, unlike the passing-by-value fashion.

) C++ use '&' for declaring references:

int rats;
int & rodents = rats;

In this way, "int &" is an identifier means reference to int, so rodents is a reference to rats and they are exactly the same, no matter value or address.

) One should initialize a reference variable when declare it. Unlike pointers, reference doesn't support later assignment.

 

int rats;
int & rodents = rats;
int bunnies;
rodents = bunnies;

 

The last line above doesn't make rodents reference to bunnies, but it actually works as "rats = bunnies".

) Take the function swap() which swaps two values for example, using reference in functions(compared to pointers and value):

void swapr(int & a, int & b); // function prototype for reference
swapr(a, b) // function call for reference
void swapp(int * a, int * b); // function prototype for pointer
swapp(&a, &b) // function call for pointer
void swapv(int a, int b); // function prototype for value
swapv(a, b) // function call for value