Where does this memory leak come from?
In my implementation of ArrayList I have a method for resizing the array. It looks like this:
template<typename T>
int ArrayList<T>::changeSize(int newsize)
{
T* tmp = (T*)(T*)realloc(internal_array,sizeof(T)*newsize);
if(tmp == NULL)
{
return 0;
}
internal_array=tmp;
Capacity = newsize;
return 1;
}
This part of code causes a memory leak when using it, any idea, what could be wrong here?
EDIT: Handling realloc being NULL still didn't help, updated the code and added adress sanitizer output:
=================================================================
==4615==ERROR: LeakSanitizer: detected memory leaks
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b6939c4 in ArrayList<int>::Add(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x29c4)
#3 0x557b3b692671 in readInput(ArrayList<int>*) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1671)
#4 0x557b3b693339 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2339)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
Direct leak of 4 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b693e0b in ArrayList<int>::Remove(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2e0b)
#3 0x557b3b692d07 in findMinDistances(ArrayList<int>) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1d07)
#4 0x557b3b6934a3 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x24a3)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
SUMMARY: AddressSanitizer: 20 byte(s) leaked in 2 allocation(s).
c++ memory memory-leaks dynamic-memory-allocation realloc
edited Nov 21 at 13:49
Swordfish
1
asked Nov 21 at 2:02
Michal Dvořák
1126
|
show 2 more comments
In my implementation of ArrayList I have a method for resizing the array. It looks like this:
template<typename T>
int ArrayList<T>::changeSize(int newsize)
{
T* tmp = (T*)(T*)realloc(internal_array,sizeof(T)*newsize);
if(tmp == NULL)
{
return 0;
}
internal_array=tmp;
Capacity = newsize;
return 1;
}
This part of code causes a memory leak when using it, any idea, what could be wrong here?
EDIT: Handling realloc being NULL still didn't help, updated the code and added adress sanitizer output:
=================================================================
==4615==ERROR: LeakSanitizer: detected memory leaks
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b6939c4 in ArrayList<int>::Add(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x29c4)
#3 0x557b3b692671 in readInput(ArrayList<int>*) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1671)
#4 0x557b3b693339 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2339)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
Direct leak of 4 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b693e0b in ArrayList<int>::Remove(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2e0b)
#3 0x557b3b692d07 in findMinDistances(ArrayList<int>) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1d07)
#4 0x557b3b6934a3 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x24a3)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
SUMMARY: AddressSanitizer: 20 byte(s) leaked in 2 allocation(s).
c++ memory memory-leaks dynamic-memory-allocation realloc
edited Nov 21 at 13:49
Swordfish
1
asked Nov 21 at 2:02
Michal Dvořák
1126
1
How do you determine that it leaks? What do you do ifrealloc()fails? Curious: what isT?
– Swordfish
Nov 21 at 2:08
3
The correct way to call realloc is to save the return value in a temporary variable and check it for NULL. That way if realloc has failed, you haven't lost your original memory, like in this answer: stackoverflow.com/a/44789446/1212725
– bruceg
Nov 21 at 2:21
@Swordfish, it's a generic type, but in my program it's an integer (int)
– Michal Dvořák
Nov 21 at 11:03
Updated my question, checking the realloc isNULLdidn't help.
– Michal Dvořák
Nov 21 at 11:20
Are you sure thatinternal_arrayholds eitherNULLor a valid pointer value returned bymalloc(),calloc(),realloc(NULL, ...)before you callrealloc()with it as the firest parameter?
– Swordfish
Nov 21 at 13:42
|
show 2 more comments
In my implementation of ArrayList I have a method for resizing the array. It looks like this:
template<typename T>
int ArrayList<T>::changeSize(int newsize)
{
T* tmp = (T*)(T*)realloc(internal_array,sizeof(T)*newsize);
if(tmp == NULL)
{
return 0;
}
internal_array=tmp;
Capacity = newsize;
return 1;
}
This part of code causes a memory leak when using it, any idea, what could be wrong here?
EDIT: Handling realloc being NULL still didn't help, updated the code and added adress sanitizer output:
=================================================================
==4615==ERROR: LeakSanitizer: detected memory leaks
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b6939c4 in ArrayList<int>::Add(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x29c4)
#3 0x557b3b692671 in readInput(ArrayList<int>*) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1671)
#4 0x557b3b693339 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2339)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
Direct leak of 4 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b693e0b in ArrayList<int>::Remove(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2e0b)
#3 0x557b3b692d07 in findMinDistances(ArrayList<int>) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1d07)
#4 0x557b3b6934a3 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x24a3)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
SUMMARY: AddressSanitizer: 20 byte(s) leaked in 2 allocation(s).
c++ memory memory-leaks dynamic-memory-allocation realloc
edited Nov 21 at 13:49
Swordfish
1
asked Nov 21 at 2:02
Michal Dvořák
1126
In my implementation of ArrayList I have a method for resizing the array. It looks like this:
template<typename T>
int ArrayList<T>::changeSize(int newsize)
{
T* tmp = (T*)(T*)realloc(internal_array,sizeof(T)*newsize);
if(tmp == NULL)
{
return 0;
}
internal_array=tmp;
Capacity = newsize;
return 1;
}
This part of code causes a memory leak when using it, any idea, what could be wrong here?
EDIT: Handling realloc being NULL still didn't help, updated the code and added adress sanitizer output:
=================================================================
==4615==ERROR: LeakSanitizer: detected memory leaks
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b6939c4 in ArrayList<int>::Add(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x29c4)
#3 0x557b3b692671 in readInput(ArrayList<int>*) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1671)
#4 0x557b3b693339 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2339)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
Direct leak of 4 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b693e0b in ArrayList<int>::Remove(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2e0b)
#3 0x557b3b692d07 in findMinDistances(ArrayList<int>) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1d07)
#4 0x557b3b6934a3 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x24a3)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
SUMMARY: AddressSanitizer: 20 byte(s) leaked in 2 allocation(s).
c++ memory memory-leaks dynamic-memory-allocation realloc
c++ memory memory-leaks dynamic-memory-allocation realloc
edited Nov 21 at 13:49
Swordfish
1
asked Nov 21 at 2:02
Michal Dvořák
1126
edited Nov 21 at 13:49
Swordfish
1
asked Nov 21 at 2:02
Michal Dvořák
1126
edited Nov 21 at 13:49
Swordfish
1
edited Nov 21 at 13:49
Swordfish
1
edited Nov 21 at 13:49
Swordfish
1
1
asked Nov 21 at 2:02
Michal Dvořák
1126
asked Nov 21 at 2:02
Michal Dvořák
1126
asked Nov 21 at 2:02
Michal Dvořák
1126
1126
1
How do you determine that it leaks? What do you do ifrealloc()fails? Curious: what isT?
– Swordfish
Nov 21 at 2:08
3
The correct way to call realloc is to save the return value in a temporary variable and check it for NULL. That way if realloc has failed, you haven't lost your original memory, like in this answer: stackoverflow.com/a/44789446/1212725
– bruceg
Nov 21 at 2:21
@Swordfish, it's a generic type, but in my program it's an integer (int)
– Michal Dvořák
Nov 21 at 11:03
Updated my question, checking the realloc isNULLdidn't help.
– Michal Dvořák
Nov 21 at 11:20
Are you sure thatinternal_arrayholds eitherNULLor a valid pointer value returned bymalloc(),calloc(),realloc(NULL, ...)before you callrealloc()with it as the firest parameter?
– Swordfish
Nov 21 at 13:42
|
show 2 more comments
1
How do you determine that it leaks? What do you do ifrealloc()fails? Curious: what isT?
– Swordfish
Nov 21 at 2:08
3
The correct way to call realloc is to save the return value in a temporary variable and check it for NULL. That way if realloc has failed, you haven't lost your original memory, like in this answer: stackoverflow.com/a/44789446/1212725
– bruceg
Nov 21 at 2:21
@Swordfish, it's a generic type, but in my program it's an integer (int)
– Michal Dvořák
Nov 21 at 11:03
Updated my question, checking the realloc isNULLdidn't help.
– Michal Dvořák
Nov 21 at 11:20
Are you sure thatinternal_arrayholds eitherNULLor a valid pointer value returned bymalloc(),calloc(),realloc(NULL, ...)before you callrealloc()with it as the firest parameter?
– Swordfish
Nov 21 at 13:42
1
1
How do you determine that it leaks? What do you do if
realloc() fails? Curious: what is T?– Swordfish
Nov 21 at 2:08
How do you determine that it leaks? What do you do if
realloc() fails? Curious: what is T?– Swordfish
Nov 21 at 2:08
3
3
The correct way to call realloc is to save the return value in a temporary variable and check it for NULL. That way if realloc has failed, you haven't lost your original memory, like in this answer: stackoverflow.com/a/44789446/1212725
– bruceg
Nov 21 at 2:21
The correct way to call realloc is to save the return value in a temporary variable and check it for NULL. That way if realloc has failed, you haven't lost your original memory, like in this answer: stackoverflow.com/a/44789446/1212725
– bruceg
Nov 21 at 2:21
@Swordfish, it's a generic type, but in my program it's an integer (
int)– Michal Dvořák
Nov 21 at 11:03
@Swordfish, it's a generic type, but in my program it's an integer (
int)– Michal Dvořák
Nov 21 at 11:03
Updated my question, checking the realloc is
NULL didn't help.– Michal Dvořák
Nov 21 at 11:20
Updated my question, checking the realloc is
NULL didn't help.– Michal Dvořák
Nov 21 at 11:20
Are you sure that
internal_array holds either NULL or a valid pointer value returned by malloc(), calloc(), realloc(NULL, ...) before you call realloc() with it as the firest parameter?– Swordfish
Nov 21 at 13:42
Are you sure that
internal_array holds either NULL or a valid pointer value returned by malloc(), calloc(), realloc(NULL, ...) before you call realloc() with it as the firest parameter?– Swordfish
Nov 21 at 13:42
|
show 2 more comments
1 Answer
1
active
oldest
votes
You are reading the error wrong:
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b6939c4 in ArrayList<int>::Add(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x29c4)
#3 0x557b3b692671 in readInput(ArrayList<int>*) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1671)
#4 0x557b3b693339 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2339)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
It clearly says that the memory allocated at ArrayList<int>::changeSize(int) is the memory that leaks. It does not say what operation caused it to leak.
This means that changeSize(int) is ok. The problem lies elsewhere. You must make sure that the rule of 5 is followed:
- Destructor frees the memory.
- Copy constructor copies contents of
internal_array, not the pointer. - Assignment operator copies the contents, and not the pointer. Consider the copy-and-swap idiom.
- Move constructor copies the pointer, but nullifies the other object.
- Move assignment swaps the pointers, or assigns one pointer and frees the other.
The bug is probably due to missing, or wrong, one of the above. A good way to make it easier to catch such bugs during compile time, is to use std::unique_ptr with a custom deleter instead of freeing manually.
Please note that your code will crash and/or leak memory with anything complex, like T=vector or T=big num. You can add static_assert(std::is_trivial<T>::value); to make sure it is not instantiated with, e.g., std::map.
answered Nov 21 at 14:26
Michael Veksler
2,2921415
add a comment |
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1 Answer
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You are reading the error wrong:
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b6939c4 in ArrayList<int>::Add(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x29c4)
#3 0x557b3b692671 in readInput(ArrayList<int>*) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1671)
#4 0x557b3b693339 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2339)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
It clearly says that the memory allocated at ArrayList<int>::changeSize(int) is the memory that leaks. It does not say what operation caused it to leak.
This means that changeSize(int) is ok. The problem lies elsewhere. You must make sure that the rule of 5 is followed:
- Destructor frees the memory.
- Copy constructor copies contents of
internal_array, not the pointer. - Assignment operator copies the contents, and not the pointer. Consider the copy-and-swap idiom.
- Move constructor copies the pointer, but nullifies the other object.
- Move assignment swaps the pointers, or assigns one pointer and frees the other.
The bug is probably due to missing, or wrong, one of the above. A good way to make it easier to catch such bugs during compile time, is to use std::unique_ptr with a custom deleter instead of freeing manually.
Please note that your code will crash and/or leak memory with anything complex, like T=vector or T=big num. You can add static_assert(std::is_trivial<T>::value); to make sure it is not instantiated with, e.g., std::map.
answered Nov 21 at 14:26
Michael Veksler
2,2921415
add a comment |
You are reading the error wrong:
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b6939c4 in ArrayList<int>::Add(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x29c4)
#3 0x557b3b692671 in readInput(ArrayList<int>*) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1671)
#4 0x557b3b693339 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2339)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
It clearly says that the memory allocated at ArrayList<int>::changeSize(int) is the memory that leaks. It does not say what operation caused it to leak.
This means that changeSize(int) is ok. The problem lies elsewhere. You must make sure that the rule of 5 is followed:
- Destructor frees the memory.
- Copy constructor copies contents of
internal_array, not the pointer. - Assignment operator copies the contents, and not the pointer. Consider the copy-and-swap idiom.
- Move constructor copies the pointer, but nullifies the other object.
- Move assignment swaps the pointers, or assigns one pointer and frees the other.
The bug is probably due to missing, or wrong, one of the above. A good way to make it easier to catch such bugs during compile time, is to use std::unique_ptr with a custom deleter instead of freeing manually.
Please note that your code will crash and/or leak memory with anything complex, like T=vector or T=big num. You can add static_assert(std::is_trivial<T>::value); to make sure it is not instantiated with, e.g., std::map.
answered Nov 21 at 14:26
Michael Veksler
2,2921415
add a comment |
You are reading the error wrong:
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b6939c4 in ArrayList<int>::Add(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x29c4)
#3 0x557b3b692671 in readInput(ArrayList<int>*) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1671)
#4 0x557b3b693339 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2339)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
It clearly says that the memory allocated at ArrayList<int>::changeSize(int) is the memory that leaks. It does not say what operation caused it to leak.
This means that changeSize(int) is ok. The problem lies elsewhere. You must make sure that the rule of 5 is followed:
- Destructor frees the memory.
- Copy constructor copies contents of
internal_array, not the pointer. - Assignment operator copies the contents, and not the pointer. Consider the copy-and-swap idiom.
- Move constructor copies the pointer, but nullifies the other object.
- Move assignment swaps the pointers, or assigns one pointer and frees the other.
The bug is probably due to missing, or wrong, one of the above. A good way to make it easier to catch such bugs during compile time, is to use std::unique_ptr with a custom deleter instead of freeing manually.
Please note that your code will crash and/or leak memory with anything complex, like T=vector or T=big num. You can add static_assert(std::is_trivial<T>::value); to make sure it is not instantiated with, e.g., std::map.
answered Nov 21 at 14:26
Michael Veksler
2,2921415
You are reading the error wrong:
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x7f0c9d1b5f40 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdef40)
#1 0x557b3b693fb2 in ArrayList<int>::changeSize(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2fb2)
#2 0x557b3b6939c4 in ArrayList<int>::Add(int) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x29c4)
#3 0x557b3b692671 in readInput(ArrayList<int>*) (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x1671)
#4 0x557b3b693339 in main (/media/mdvorak/Maxtor/Vysoká Škola/PA1/progtest5/a.out+0x2339)
#5 0x7f0c9cd07b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
It clearly says that the memory allocated at ArrayList<int>::changeSize(int) is the memory that leaks. It does not say what operation caused it to leak.
This means that changeSize(int) is ok. The problem lies elsewhere. You must make sure that the rule of 5 is followed:
- Destructor frees the memory.
- Copy constructor copies contents of
internal_array, not the pointer. - Assignment operator copies the contents, and not the pointer. Consider the copy-and-swap idiom.
- Move constructor copies the pointer, but nullifies the other object.
- Move assignment swaps the pointers, or assigns one pointer and frees the other.
The bug is probably due to missing, or wrong, one of the above. A good way to make it easier to catch such bugs during compile time, is to use std::unique_ptr with a custom deleter instead of freeing manually.
Please note that your code will crash and/or leak memory with anything complex, like T=vector or T=big num. You can add static_assert(std::is_trivial<T>::value); to make sure it is not instantiated with, e.g., std::map.
answered Nov 21 at 14:26
Michael Veksler
2,2921415
answered Nov 21 at 14:26
Michael Veksler
2,2921415
answered Nov 21 at 14:26
Michael Veksler
2,2921415
answered Nov 21 at 14:26
Michael Veksler
2,2921415
2,2921415
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1
How do you determine that it leaks? What do you do if
realloc()fails? Curious: what isT?– Swordfish
Nov 21 at 2:08
3
The correct way to call realloc is to save the return value in a temporary variable and check it for NULL. That way if realloc has failed, you haven't lost your original memory, like in this answer: stackoverflow.com/a/44789446/1212725
– bruceg
Nov 21 at 2:21
@Swordfish, it's a generic type, but in my program it's an integer (
int)– Michal Dvořák
Nov 21 at 11:03
Updated my question, checking the realloc is
NULLdidn't help.– Michal Dvořák
Nov 21 at 11:20
Are you sure that
internal_arrayholds eitherNULLor a valid pointer value returned bymalloc(),calloc(),realloc(NULL, ...)before you callrealloc()with it as the firest parameter?– Swordfish
Nov 21 at 13:42