您好,登錄后才能下訂單哦!
這篇文章將為大家詳細(xì)講解有關(guān)C++中引用的示例分析,小編覺得挺實(shí)用的,因此分享給大家做個(gè)參考,希望大家閱讀完這篇文章后可以有所收獲。
在c/c++中,訪問一個(gè)變量只能通過兩種方式被訪問,傳遞,或者查詢。這兩種方式是:
1.通過值訪問/傳遞變量
2.通過地址訪問/傳遞變量–這種方法就是指針
除此之外沒有第三種訪問和傳遞變量值的方法。引用變量也就是個(gè)指針變量,它也擁有內(nèi)存空間。最關(guān)鍵的是引用是一種會(huì)被編譯器自動(dòng)解引用的指針。很難相信么?
下面是一段使用引用的簡(jiǎn)單c++代碼
#include <iostream.h> int main() { int i = 10; // A simple integer variable int &j = i; // A Reference to the variable i j++; // Incrementing j will increment both i and j. // check by printing values of i and j cout<< i << j <<endl; // should print 11 11 // Now try to print the address of both variables i and j cout<< &i << &j <<endl; // surprisingly both print the same address and make us feel that they are // alias to the same memory location. // In example below we will see what is the reality return 0; }
引用其實(shí)就是c++中的常量指針。表達(dá)式int &i = j;將會(huì)被編譯器轉(zhuǎn)化成int *const i = &j;而引用之所以要初始化是因?yàn)閏onst類型變量必須初始化,這個(gè)指針也必須有所指。下面我們?cè)俅尉劢沟缴厦孢@段代碼,并使用編譯器的那套語(yǔ)法將引用替換掉。
#include <iostream.h> int main() { int i = 10; // A simple integer variable int *const j = &i; // A Reference to the variable i (*j)++; // Incrementing j. Since reference variables are // automatically dereferenced by compiler // check by printing values of i and j cout<< i << *j <<endl; // should print 11 11 // A * is appended before j because it used to be reference variable // and it should get automatically dereferenced. return 0; }
讀者一定很奇怪為什么我上面這段代碼會(huì)跳過打印地址這步。這里需要一些解釋。因?yàn)橐米兞繒r(shí)會(huì)被編譯器自動(dòng)解引用的,那么一個(gè)諸如cout << &j << endl;的語(yǔ)句,編譯器就會(huì)將其轉(zhuǎn)化成語(yǔ)句cout << &*j << endl;現(xiàn)在&*會(huì)相互抵消,這句話變的毫無(wú)意義,而cout打印的j值就是i的地址,因?yàn)槠涠x語(yǔ)句為int *const j = &i;
所以語(yǔ)句cout << &i << &j << endl;變成了cout << &i << &*j << endl;這兩種情況都是打印輸出i的地址。這就是當(dāng)我們打印普通變量和引用變量的時(shí)候會(huì)輸出相同地址的原因。
下面給出一段復(fù)雜一些的代碼,來看看引用在級(jí)聯(lián)(cascading)中是如何運(yùn)作的。
#include <iostream.h> int main() { int i = 10; // A Simple Integer variable int &j = i; // A Reference to the variable // Now we can also create a reference to reference variable. int &k = j; // A reference to a reference variable // Similarly we can also create another reference to the reference variable k int &l = k; // A reference to a reference to a reference variable. // Now if we increment any one of them the effect will be visible on all the // variables. // First print original values // The print should be 10,10,10,10 cout<< i << "," << j << "," << k << "," << l <<endl; // increment variable j j++; // The print should be 11,11,11,11 cout<< i << "," << j << "," << k << "," << l <<endl; // increment variable k k++; // The print should be 12,12,12,12 cout<< i << "," << j << "," << k << "," << l <<endl; // increment variable l l++; // The print should be 13,13,13,13 cout<< i << "," << j << "," << k << "," << l <<endl; return 0; }
下面這段代碼是將上面代碼中的引用替換之后代碼,也就是說明我們不依賴編譯器的自動(dòng)替換功能,手動(dòng)進(jìn)行替換也能達(dá)到相同的目標(biāo)。
#include <iostream.h> int main() { int i = 10; // A Simple Integer variable int *const j = &i; // A Reference to the variable // The variable j will hold the address of i // Now we can also create a reference to reference variable. int *const k = &*j; // A reference to a reference variable // The variable k will also hold the address of i because j // is a reference variable and // it gets auto dereferenced. After & and * cancels each other // k will hold the value of // j which it nothing but address of i // Similarly we can also create another reference to the reference variable k int *const l = &*k; // A reference to a reference to a reference variable. // The variable l will also hold address of i because k holds address of i after // & and * cancels each other. // so we have seen that all the reference variable will actually holds the same // variable address. // Now if we increment any one of them the effect will be visible on all the // variables. // First print original values. The reference variables will have * prefixed because // these variables gets automatically dereferenced. // The print should be 10,10,10,10 cout<< i << "," << *j << "," << *k << "," << *l <<endl; // increment variable j (*j)++; // The print should be 11,11,11,11 cout<< i << "," << *j << "," << *k << "," << *l <<endl; // increment variable k (*k)++; // The print should be 12,12,12,12 cout<< i << "," << *j << "," << *k << "," << *l <<endl; // increment variable l (*l)++; // The print should be 13,13,13,13 cout << i << "," << *j << "," << *k << "," << *l <<endl; return 0; }
我們通過下面代碼可以證明c++的引用不是神馬別名,它也會(huì)占用內(nèi)存空間的。
#include <iostream.h> class Test { int &i; // int *const i; int &j; // int *const j; int &k; // int *const k; }; int main() { // This will print 12 i.e. size of 3 pointers cout<< "size of class Test = " << sizeof(class Test) <<endl; return 0; }
我希望這篇文章能把c++引用的所有東東都解釋清楚,然而我要指出的是c++標(biāo)準(zhǔn)并沒有解釋編譯器如何實(shí)現(xiàn)引用的行為。所以實(shí)現(xiàn)取決于編譯器,而大多數(shù)情況下就是將引用實(shí)現(xiàn)為一個(gè)const指針。
引用支持c++虛函數(shù)機(jī)制的代碼
#include <iostream.h> class A { public: virtual void print() { cout<<"A.."<<endl; } }; class B : public A { public: virtual void print() { cout<<"B.."<<endl; } }; class C : public B { public: virtual void print() { cout<<"C.."<<endl; } }; int main() { C c1; A &a1 = c1; a1.print(); // prints C A a2 = c1; a2.print(); // prints A return 0; }
關(guān)于“C++中引用的示例分析”這篇文章就分享到這里了,希望以上內(nèi)容可以對(duì)大家有一定的幫助,使各位可以學(xué)到更多知識(shí),如果覺得文章不錯(cuò),請(qǐng)把它分享出去讓更多的人看到。
免責(zé)聲明:本站發(fā)布的內(nèi)容(圖片、視頻和文字)以原創(chuàng)、轉(zhuǎn)載和分享為主,文章觀點(diǎn)不代表本網(wǎng)站立場(chǎng),如果涉及侵權(quán)請(qǐng)聯(lián)系站長(zhǎng)郵箱:is@yisu.com進(jìn)行舉報(bào),并提供相關(guān)證據(jù),一經(jīng)查實(shí),將立刻刪除涉嫌侵權(quán)內(nèi)容。