C ++ reference

C ++ reference

This article mainly records the reference features in C ++ and summarizes the sample code and errors.

When creating a reference, you must specify the referenced object, and the referenced object will not be modified in the future. A reference is equivalent to a variable alias.

# Include <iostream> # include <string. h> using namespace std; void swapOne (char * & x, char * & y) // pointer reference {char * temp; temp = x; x = y; y = temp;} void swapTwo (char ** x, char ** y) // pointer {char * temp; temp = * x; * x = * y; * y = temp;} void swapThree (char * x, char * y) // pass the pointer value (this method does not work, it is equivalent to passing the value) {// someone may misunderstand this because two integers may have been exchanged using pointers. This is quite different. Char * temp; temp = x; x = y; y = temp;} int main () {char * ap = "Hello"; // * ap content is H, * The content of bp is H char * bp = "How are you? "; Cout <" ap: "<ap <endl; cout <" bp: "<bp <endl; // swapOne (ap, bp ); // swapTwo (& ap, & bp); swapThree (ap, bp); cout <"swap ap, bp" <endl; cout <"ap: "<ap <endl; cout <" bp: "<bp <endl; return 0 ;}# Include <iostream> using namespace std; const float pi = 3.14f; // constant float f; // global variable float f1 (float r) {f = r * pi; return f;} float & f2 (float r) // return reference {f = r * pi; return f; // return the reference of the local variable (note the validity period ), the system runs normally, but the result is incorrect. /* Float ff = f; return ff; */} int main () {float f1 (float = 5); // default parameter 5, you can modify the global variable f = 78.5 float & f2 (float = 5); // same as float a = f1 (); // float & B = f1 (); // In the f1 () function, the value of global variable f is 78.1 assigned to a temporary variable temp (which is implicitly created by the compiler), and then reference B of this temp, an error occurs when referencing a temporary variable temp. float c = f2 (); float & d = f2 (); // The definition variable is not used in the main function, instead, use the reference of global variables directly. This method saves the most memory space among all 4 methods. However, pay attention to the validity period it references. // The validity period of the global variable f must be longer than the reference d, so it is safe. For example, return a reference to a local variable. D + = 1.0f; cout <"a =" <a <endl; // cout <"B =" <B <endl; cout <"c =" <c <endl; cout <"d =" <d <endl; cout <"f =" <f <endl; return 0 ;}# Include <iostream> using namespace std; class Test {public: void f (const int & arg); private: int value ;}; int main () {int a = 7; const int B = 10; // int & c = B; // error: B is a constant, but C is not a constant reference. Correct: const int & c = B; const int & d = a; a ++; // d ++; // error. d is a constant reference. Therefore, Test test; test cannot be modified. f (a); cout <"a =" <a <endl; return 0;} void Test: f (const int & arg) {// arg = 10; // The cout <"arg =" <arg <endl; value = 20 ;}/ For a variable of the constant type, its reference must also be of the constant type. * Variables of a non-constant type can be non-constants. * However, note: under no circumstances can constant references be used to modify the value of referenced variables. */