C + + anonymous namespace--anonymous space

C + + anonymous namespace--anonymous space

Anonymous space, anonymous class, anonymous consortium, anonymous struct. Anonymous space

2. #include <stdio. h>
   
6. Namespace A {
   
8. int ID = 1;
   
10. }
    
12. Namespace {
    
14. int ID = one;
    
16. }
    
20. Namespace B {
    
22. int ID = +;
    
24. }
    
28. int main(void){
    
30. printf("id%d \ n", id);
    
32. }

Output

1. ID 11

The function of C is used here to reduce the disturbance of STD space. The output here is the contents of the anonymous space. Then it is similar to the following usage

1. Namespace __unique_name_ {
2. int ID;
3. }
   
4. using namespace __unique_name_;

If you modify the code as follows

2. #include <stdio. h>
   
6. Namespace A {
   
8. int ID = 1;
   
10. }
    
12. Namespace {
    
14. int ID = one;
    
16. }
    
20. Namespace B {
    
22. int ID = +;
    
24. }
    
26. Namespace {
    
28. int ID = a;
    
30. }
    
34. int main(void){
    
36. printf("id%d \ n", id);
    
38. }

compile the error, as follows

1. T_anonymity_space.cpp:14:error:redefinition of ' int:: ID '
2. T_anonymity_space.cpp:7: Error: ' int:: ID ' previously defined here

In a different file?

1. File def.h
2. Namespace {
   
3. int ID = a;
   
4. }

2. #include <stdio. h>
   
4. #include "Def.h"
   
6. Namespace A {
   
8. int ID = 1;
   
10. }
    
12. Namespace {
    
14. int ID = one;
    
16. }
    
20. Namespace B {
    
22. int ID = +;
    
24. }
    
28. int main(void){
    
30. printf("id%d \ n", id);
    
32. }

Compile error

1. T_anonymity_space.cpp:7: Error:redefinition of ' int:: ID '
2. Def.h:3: Error: ' int:: ID ' previously defined here

This shows that anonymous namespace is in a space. References to other spaces later usage

2. #include <stdio. h>
   
4. Namespace A {
   
6. int ID = 1;
   
8. }
   
10. Namespace {
    
12. int ID = one;
    
14. int id =n;
16. }
    
20. Namespace B {
    
22. int ID = +;
    
24. }
    
28. int main(void){
    
30. printf("id%d \ n", id);
    
34. using namespace A;
    
36. printf("id%d-%d-%d \ n", A:: ID, :: ID, id);
    
40. }

Output

1. ID 11
2. ID 1-11-12

Other spaces are referenced, and at this point if the use of anonymous space is in the same space, and the same name must be added:: To differentiate. I guess here, is the global variable in the default anonymous space? Judging from the phenomenon, probably is.

C + + anonymous namespace--anonymous space