Fork#40686: std::string custom operator new/delete function
Open Date: 2020-08-30 10:32
Last Update: 2020-09-02 14:10
URL for this Ticket:
https://osdn.net//projects/mingw/ticket/40686
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Last Changes/Comment on this Ticket:
2020-09-02 14:10 Updated by: keith
* Resolution Update from None to Works For Me
* Severity Update from 5 - Medium to 1 - Lowest
* Priority Update from 5 - Medium to 1 - Lowest
Comment:
This is an issue which really would have been better to raise on the mailing
list, where it would be visible to a broader spectrum of experienced users. My
own expertise is predominantly in FORTRAN-77 and C programming; my knowledge of
C++ is sketchy, at best. Nonetheless, I will try to answer, to the best of my
ability.
Firstly, let me make it perfectly clear: any comparison between behaviour on
Windows, and behaviour on Linux, is completely irrelevant; the two platforms
are fundamentally different, and there are many pitfalls in migrating from
either one to the other. In this case, I believe you are falling foul of one of
those pitfalls; there is no bug here, beyond a gap in your understanding.
In your test case, while you define replacements for both new and delete, I see
no explicit use of either; any use which does arise is implicit in the
instantiation, and subsequent destruction, of the std::string object, to which
you refer. Instantiation of that object, apparently, does invoke new, and
destruction thus invokes delete, but consider this: where is the implementation
of that std::string class object defined? I'll give you some time to think
about that, then I'll suggest, in follow-up comments, how the answer may
explain the behaviour you have observed.
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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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