Fork#40686: std::string custom operator new/delete function
Open Date: 2020-08-30 18:32
Last Update: 2020-09-03 15:31
URL for this Ticket:
https://osdn.net//projects/mingw/ticket/40686
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Last Changes/Comment on this Ticket:
2020-09-03 15:31 Updated by: marvol
Comment:
Thank you for your reply.
It is possible that I am missing something. I understand that std::string can
have own implementation of allocation of the data. I think that in the current
libstdc++ implementation if a length of the string is greater than 15 bytes,
then it uses the heap for allocation.
On line 43, there is an assignment operator for the string and this string is
long enough to allocate string data on the heap. On the next line the object
"obj" ends its lifetime so "obj" destructor is called, also with std::string
destructor which releases the string data.
For me it is strange that there is no 1 to 1 relation between calling operator
new/delete (how should I release memory that was not allocated in my
allocator?). I tried other containers like std::vector and they seem to be
consistent.
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Ticket Status:
Reporter: marvol
Owner: (None)
Type: Issues
Status: Open
Priority: 1 - Lowest
MileStone: (None)
Component: GCC
Severity: 1 - Lowest
Resolution: Works For Me
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Ticket details:
Hello,
I am writing a custom wrapper for new/delete allocations to get an aligned
memory. I noticed that if I use std::string, operator new/delete are not called
as it is in a linux version of g++ (operators new/delete are called). With the
default optimization level, operator new/delete is not called and with
optimization levels O1, O2, O3 only operator delete is called.
Source:
1. #include <string>
2. #include <cstdio>
3. #include <cstdlib>
4.
5. void* operator new(size_t size)
6. {
7. printf("Calling new: %zu", size);
8. void* address = malloc(size);
9.
10. printf(" address: 0x%p\n", address);
11. return address;
12. }
13.
14. void* operator new[](size_t size)
15. {
16. printf("Calling new[]: %zu", size);
17. void* address = malloc(size);
18.
19. printf(" address: 0x%p\n", address);
20. return address;
21. }
22.
23. void operator delete(void* address)
24. {
25. printf("Calling delete, address: 0x%p\n", address);
26. free(address);
27. }
28.
29. void operator delete[](void* address)
30. {
31. printf("Calling delete[], address: 0x%p\n", address);
32. free(address);
33. }
34.
35. struct Obj
36. {
37. std::string m_str;
38. };
39.
40. void test()
41. {
42. Obj obj;
43. obj.m_str = "long string ......................";
44. }
45.
46. int main()
47. {
48. test();
49.
50. return 0;
51. }
Compiling with the default optimization level:
• g++ main.cpp -std=c++11 -o test.exe
Output:
• NONE
Compiling with the O2 optimization level:
• g++ main.cpp -std=c++11 -O2 -o test.exe
Output:
• Calling delete, address: 0x00542098
I am using:
• OS: Windows 7
• Mingw: 5.4.1
• Shell: cmd MINGW32_NT-6.1 MARTIN-LENOVO 1.0.18(0.48/3/2) 2012-11-21 22:34
i686 Msys
• Uname -a:
• G++: g++ (MinGW.org GCC Build-2) 9.2.0
• GCC: gcc (MinGW.org GCC Build-2) 9.2.0
• ld: GNU ld (GNU Binutils) 2.32
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