list中的erase和remove

冷不防 2022-06-10 09:40 317阅读 0赞

erase的作用是，使作为参数的迭代器失效，并返回指向该迭代器下一参数的迭代器。

如下：

**\[cpp\]**  view plain  copy

print ?

1.  list ParticleSystem;
2.  
3.  list::iterator pointer;
4.  
5.  if(pointer->dead == true)
6.  \{
7.  pointer = ParticleSystem.erase(pointer);
8.  \}

list ParticleSystem;
    
    list::iterator pointer;
    
    if(pointer->dead == true)
    {
       pointer = ParticleSystem.erase(pointer);
    }

有一段关于错误使用erase的程序

**\[cpp\]**  view plain  copy

print ?

1.  using namespace std;
2.  int main()
3.  \{
4.  std::listtest\_list;
5.  std::list::iterator test\_list\_it;
6.  
7.  test\_list.push\_back(1);
8.  
9.  test\_list\_it = test\_list.begin();
10. for(;test\_list\_it != test\_list.end();test\_list\_it++)
11. 
12. \{
13. test\_list.erase(test\_list\_it);
14. \}
15. \}

using namespace std;
    int main()
    {
      std::listtest_list;
      std::list::iterator test_list_it;
    
      test_list.push_back(1);
    
      test_list_it = test_list.begin();
      for(;test_list_it != test_list.end();test_list_it++)
    
      {
      test_list.erase(test_list_it);
      }
    }

问题：该程序不能跳出循环

原因：test\_list.erase(test\_list\_it);每次做erase时都有可能使迭代器失效，test\_list\_it++就发生错误了。可以参见effective stl一书。所有容器做erase操作时都有可能使迭代器失效。

改为：

**\[html\]**  view plain  copy

print ?

1.  for(;test\_list\_it != test\_list.end();)
2.  \{
3.  test\_list.erase(test\_list\_it++);
4.  \}

for(;test_list_it != test_list.end();)
    {
        test_list.erase(test_list_it++);
    }

**\[cpp\]**  view plain  copy

print ?

1.  for(;test\_list\_it != test\_list.end();)
2.  \{
3.  std::list::iterator iter\_e=test\_list\_it++;
4.  test\_list.erase(iter\_e);
5.  \}

for(;test_list_it != test_list.end();)
    {
        std::list::iterator iter_e=test_list_it++;
        test_list.erase(iter_e);
    }

注意：

**\[cpp\]**  view plain  copy

print ?

1.  for(;test\_list\_it != test\_list.end();test\_list\_it++;) \{
2.  std::list::iterator iter\_e=test\_list\_it;
3.  test\_list.erase(iter\_e);
4.  \}

for(;test_list_it != test_list.end();test_list_it++;) {
        std::list::iterator iter_e=test_list_it;
        test_list.erase(iter_e);
    }

这样仍然是错误的，原因是：iter\_e=test\_list\_it 是指针值的复制，它俩其实指向同一个位置，所以iter\_e失效那么test\_list\_it也会失效，所以test\_list\_it++就会有问题  
如果是

**\[cpp\]**  view plain  copy

print ?

1.  for(;test\_list\_it != test\_list.end();)
2.  \{
3.  std::list::iterator iter\_e=test\_list\_it++;
4.  test\_list.erase(iter\_e);
5.  \}

for(;test_list_it != test_list.end();)
    {
        std::list::iterator iter_e=test_list_it++;
        test_list.erase(iter_e);
    }

则没有问题。

以上转自：[http://blog.sina.com.cn/s/blog\_782496390100rtyp.html][http_blog.sina.com.cn_s_blog_782496390100rtyp.html]

remove函数也存在erase函数同样的问题，但remove函数返回值是空，erase返回指向下一个元素的迭代器。

下面是一个简单的例子。

**\[cpp\]**  view plain  copy

print ?

1.  \#include "stdafx.h"
2.  \#include <stdio.h>
3.  \#include <string.h>
4.  
5.  \#include <malloc.h>
6.  \#include <list>
7.  
8.  using namespace std;
9.  
10. int \_tmain(int argc, \_TCHAR\* argv\[\])
11. \{
12. printf("------------------------------ Start\\n");
13. 
14. list<int> ls;
15. 
16. printf("ls.empty() = %d \\n", ls.empty());
17. printf("ls.max\_size() = %d \\n", ls.max\_size());
18. printf("ls.size() = %d \\n", ls.size());
19. 
20. ls.push\_back(1);
21. ls.push\_back(2);
22. ls.push\_back(3);
23. printf("\\n--------- after push 1, 2, 3 ---------\\n");
24. printf("ls.empty() = %d \\n", ls.empty());
25. printf("ls.max\_size() = %d \\n", ls.max\_size());
26. printf("ls.size() = %d \\n", ls.size());
27. for (list<int>::iterator i = ls.begin(); i != ls.end(); i++) \{
28. printf("%d, ", \*i);
29. \}
30. 
31. printf("\\n------------------------------\\n");
32. for (list<int>::iterator i = ls.begin(); i != ls.end(); ) \{
33. printf("erase %d \\n", \*i);
34. ls.erase(i++);
35. \}
36. printf("\\n--------- after erase ---------\\n");
37. printf("ls.empty() = %d \\n", ls.empty());
38. printf("ls.max\_size() = %d \\n", ls.max\_size());
39. printf("ls.size() = %d \\n", ls.size());
40. 
41. printf("\\n------------------------------\\n");
42. ls.push\_back(1);
43. ls.push\_back(2);
44. ls.push\_back(3);
45. for (list<int>::iterator i = ls.begin(); i != ls.end(); ) \{
46. printf("remove %d \\n", \*i);
47. ls.remove(\*i++);
48. \}
49. printf("\\n--------- after remove ---------\\n");
50. 
51. printf("ls.empty() = %d \\n", ls.empty());
52. printf("ls.max\_size() = %d \\n", ls.max\_size());
53. printf("ls.size() = %d \\n", ls.size());
54. 
55. printf("\\n------------------------------ End\\n");
56. getchar();
57. return 0;
58. \}

#include "stdafx.h"
    #include <stdio.h>
    #include <string.h>
    
    #include <malloc.h>
    #include <list>
    
    using namespace std;
    
    int _tmain(int argc, _TCHAR* argv[])
    {
    	printf("------------------------------ Start\n");
    
    	list<int> ls;
    
    	printf("ls.empty() = %d \n", ls.empty());
    	printf("ls.max_size() = %d \n", ls.max_size());
    	printf("ls.size() = %d \n", ls.size());
    
    	ls.push_back(1);
    	ls.push_back(2);
    	ls.push_back(3);
    	printf("\n--------- after push 1, 2, 3 ---------\n");
    	printf("ls.empty() = %d \n", ls.empty());
    	printf("ls.max_size() = %d \n", ls.max_size());
    	printf("ls.size() = %d \n", ls.size());
    	for (list<int>::iterator i = ls.begin(); i != ls.end(); i++) {
    		printf("%d, ", *i);
    	}
    
    	printf("\n------------------------------\n");
    	for (list<int>::iterator i = ls.begin(); i != ls.end(); ) {
    		printf("erase %d \n", *i);
    		ls.erase(i++);
    	}
    	printf("\n--------- after erase ---------\n");
    	printf("ls.empty() = %d \n", ls.empty());
    	printf("ls.max_size() = %d \n", ls.max_size());
    	printf("ls.size() = %d \n", ls.size());
    
    	printf("\n------------------------------\n");
    	ls.push_back(1);
    	ls.push_back(2);
    	ls.push_back(3);
    	for (list<int>::iterator i = ls.begin(); i != ls.end(); ) {
    		printf("remove %d \n", *i);
    		ls.remove(*i++);
    	}
    	printf("\n--------- after remove ---------\n");
    
    	printf("ls.empty() = %d \n", ls.empty());
    	printf("ls.max_size() = %d \n", ls.max_size());
    	printf("ls.size() = %d \n", ls.size());
    
    	printf("\n------------------------------ End\n");
    	getchar();
    	return 0;
    }

其中:

**\[cpp\]**  view plain  copy

print ?

1.  for (list<int>::iterator i = ls.begin(); i != ls.end(); ) \{
2.  printf("erase %d \\n", \*i);
3.  ls.erase(i++);
4.  \}

for (list<int>::iterator i = ls.begin(); i != ls.end(); ) {
    		printf("erase %d \n", *i);
    		ls.erase(i++);
    	}

也可以写成下面的形式，因为erase函数的返回值就是指向下一个元素的迭代器。

**\[cpp\]**  view plain  copy

print ?

1.  for (list<int>::iterator i = ls.begin(); i != ls.end(); ) \{
2.  printf("erase %d \\n", \*i);
3.  i = ls.erase(i);
4.  \}

for (list<int>::iterator i = ls.begin(); i != ls.end(); ) {
    		printf("erase %d \n", *i);
    		i = ls.erase(i);
    	}

输出结果如下：

\------------------------------ Start  
ls.empty() = 1  
ls.max\_size() = 1073741823  
ls.size() = 0

\--------- after push 1, 2, 3 ---------  
ls.empty() = 0  
ls.max\_size() = 1073741823  
ls.size() = 3  
1, 2, 3,  
\------------------------------  
erase 1  
erase 2  
erase 3

\--------- after erase ---------  
ls.empty() = 1  
ls.max\_size() = 1073741823  
ls.size() = 0

\------------------------------  
remove 1  
remove 2  
remove 3

\--------- after remove ---------  
ls.empty() = 1  
ls.max\_size() = 1073741823  
ls.size() = 0

\------------------------------ End

[http_blog.sina.com.cn_s_blog_782496390100rtyp.html]: http://blog.sina.com.cn/s/blog_782496390100rtyp.html