&i Considerations for int i and int in C + +

Source: http://blog.csdn.net/qianchenglenger/article/details/16949689

1.int I-value, int & I-pass reference

int I does not return parameters, and int &i can be returned with parameters, such as

[CPP]View PlainCopy 

2. #include <iostream>
6. void test1 (int i)
8. {
10. i = 7;
12. }
16. void Test2 (int &i) //To limit parameter changes, you can add a const limit
18. {
20. i = 7;
22. }
26. int main ()
28. {
30. int t1 = 10;
32. Test1 (t1);
34. Std::cout << T1 << Std::endl; //output is ten
38. int t2 = 10;
40. Test2 (T2);
42. Std::cout << T2 << Std::endl; //output is 7
46. return 0;
48. }

2. int I can assign constants, and int & I cannot

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2. #include <iostream>
6. void test1 (int i)
8. {
10. i = 7;
12. }
16. void Test2 (int &i)
18. {
20. i = 7;
22. }
26. int main ()
28. {
30. int i = 10; //Legal
32. int &i1 = 10; //Compilation error
36. Test1 (10); //Legal
38. Test2 (10); //Compilation error
42. return 0;
44. }

3. int &i is equivalent to an alias, and int i is just a copy

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2. #include <iostream>
6. int main ()
8. {
10. int t1 = 10;
12. int t2 = 10;
14. int i1 = t1; //Copy
16. int &i2 = t2; //Aliases
20. I1 = 7;
22. I2 = 7;
26. Std::cout << T1 << Std::endl; //Output ten
28. Std::cout << T2 << Std::endl; //Output 7
32. return 0;
34. }

Finally, let's take a look at another example

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2. #include <iostream>
4. Class a{
6. Public
8. A (int a, int b): I1 (a), i2 (b) {};
12. Public
14. int i1;
16. int &i2;
18. };
22. int main ()
24. {
26. A (45,60);
28. Std::cout << a.i1 << "<< a.i2 << Std::endl;
30. return 0;
32. }

After running on the computer, you will find that the first number is normal, and the second number is obviously an undefined value, for example, I get the result after running

45 1400458944

This is because when we construct an object, we call the constructor, and the argument to the constructor of a is passed as a value, so when called, it is equivalent to having a

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1. int B = 60

I2 (b) is the equivalent of [CPP]View PlainCopy 

1. int &i2 = b;

When the constructor call is complete, the scope of B is ended, B is destroyed, and i2 points to a place that has been destroyed, an undefined run result appears.
We're going to post a procedure that corresponds to the previous paragraph, but this time we'll get 45 60 results.
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2. #include <iostream>
4. Class a{
6. Public
8. A (int a, int &b): I1 (a), i2 (b) {};
12. Public
14. int i1;
16. int &i2;
18. };
22. int main ()
24. {
26. int t = 60;
28. A (45,t);
30. Std::cout << a.i1 << "<< a.i2 << Std::endl;
32. return 0;
34. }

&i Considerations for int i and int in C + +