How to find memory leak in a C code project

Question

I am a C   programmer on the Windows platform  I am using Visual Studio 2008   I usually end up in the code with memory leaks   Normally I find the memory leak by inspecting the code  but it is cumbersome and is not always a good approach      Since I can t afford a paid memory leak detection tool  I wanted you guys to suggest the best possible ways to avoid memory leaks    I want to the know how the programmer can find memory leaks  Is there any standard or procedure one should follow to ensure there is no memory leak in the program

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Visual Leak Detector  VLD  is a free  robust  open-source memory leak detection system for Visual C        When you run your program under the Visual Studio debugger  Visual Leak Detector will output a memory leak report at the end of your debugging session  The leak report includes the full call stack showing how any leaked memory blocks were allocated  Double-click on a line in the call stack to jump to that file and line in the editor window    If you only have crash dumps  you can use the Windbg  heap -l command  it will detect leaked heap blocks  Better open the gflags option     Create user mode stack trace database     then you will see the memory allocation call stack

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AddressSanitizer  ASan  is a fast memory error detector   It finds use-after-free and  heap stack global -buffer overflow bugs in C C   programs  It finds    Use after free  dangling pointer dereference   Heap buffer overflow Stack buffer overflow  Global buffer overflow  Use after return Initialization order bugs   This tool is very fast  The average slowdown of the instrumented program is  2x

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Download Debugging Tools for Windows  Use the gflags utility to turn on user-mode stack traces  Use UMDH to take multiple snapshots of your program s memory  Take a snapshot before memory gets allocated  and take a second snapshot after a point at which you believe that your program has leaked memory  You might want to add pauses or prompts in your program to give you a chance to run UMDH and take the snapshots  Run UMDH again  this time in its mode that does a diff between the two snapshots  It will then generate a report containing the call stacks of suspected memory leaks  Restore your previous gflags settings when you re done    UMDH will give you more information than the CRT debug heap because it is watching memory allocations across your entire process  it can even tell you if third-party components are leaking

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You can use some techniques in your code to detect memory leak  The most common and most easy way to detect is  define a macro say  DEBUG NEW and use it  along with predefined macros like   FILE   and   LINE   to locate the memory leak in your code  These predefined macros tell you the file and line number of memory leaks   DEBUG NEW is just a MACRO which is usually defined as    define DEBUG NEW new   FILE      LINE     define new DEBUG NEW   So that wherever you use new  it also can keep track of the file and line number which could be used to locate memory leak in your program   And   FILE      LINE   are predefined macros which evaluate to the filename and line number respectively where you use them   Read the following article which explains the technique of using DEBUG NEW with other interesting macros  very beautifully   A Cross-Platform Memory Leak Detector    From Wikpedia      Debug new refers to a technique in C     to overload and or redefine operator   new and operator delete in order to   intercept the memory allocation and   deallocation calls  and thus debug a   program for memory usage  It often   involves defining a macro named   DEBUG NEW  and makes new become   something like new  FILE    LINE     to record the file line information on   allocation  Microsoft Visual C   uses   this technique in its Microsoft   Foundation Classes  There are some   ways to extend this method to avoid   using macro redefinition while still   able to display the file line   information on some platforms  There   are many inherent limitations to this   method  It applies only to C    and   cannot catch memory leaks by C   functions like malloc  However  it can   be very simple to use and also very   fast  when compared to some more   complete memory debugger solutions

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Answering the second part of your question       Is there any standard or procedure one should follow to ensure there is no memory leak in the program    Yes  there is  And this is one of the key differences between C and C     In C    you should never call new or delete in your user code  RAII is a very commonly used technique  which pretty much solves the resource management problem  Every resource in your program  a resource is anything that has to be acquired  and then later on  released  file handles  network sockets  database connections  but also plain memory allocations  and in some cases  pairs of API calls  BeginX   EndX    LockY    UnlockY     should be wrapped in a class  where    the constructor acquires the resource  by calling new if the resource is a memroy allocation  the destructor releases the resource  copying and assignment is either prevented  by making the copy constructor and assignment operators private   or are implemented to work correctly  for example by cloning the underlying resource    This class is then instantiated locally  on the stack  or as a class member  and not by calling new and storing a pointer    You often don t need to define these classes yourself  The standard library containers behave in this way as well  so that any object stored into a std  vector gets freed when the vector is destroyed  So again  don t store a pointer into the container  which would require you to call new and delete   but rather the object itself  which gives you memory management for free   Likewise  smart pointer classes can be used to easily wrap objects that just have to be allocated with new  and control their lifetimes   This means that when the object goes out of scope  it is automatically destroyed  and its resource released and cleaned up   If you do this consistently throughout your code  you simply won t have any memory leaks  Everything that could get leaked is tied to a destructor which is guaranteed to be called when control leaves the scope in which the object was declared

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Instructions  Things You ll Need   Proficiency in C   C   compiler Debugger and other investigative software tools   1  Understand the operator basics  The C   operator new allocates heap memory  The delete operator frees heap memory  For every new  you should use a delete so that you free the same memory you allocated   char  str   new char  30      Allocate 30 bytes to house a string   delete    str     Clear those 30 bytes and make str point nowhere    2  Reallocate memory only if you ve deleted  In the code below  str acquires a new address with the second allocation  The first address is lost irretrievably  and so are the 30 bytes that it pointed to  Now they re impossible to free  and you have a memory leak   char  str   new char  30      Give str a memory address      delete    str     Remove the first comment marking in this line to correct   str   new char  60      Give str another memory address with                                                     the first one gone forever     delete    str     This deletes the 60 bytes  not just the first 30    3  Watch those pointer assignments  Every dynamic variable  allocated memory on the heap  needs to be associated with a pointer  When a dynamic variable becomes disassociated from its pointer s   it becomes impossible to erase  Again  this results in a memory leak   char  str1   new char  30    char  str2   new char  40    strcpy str1   Memory leak     str2   str1     Bad  Now the 40 bytes are impossible to free   delete    str2     This deletes the 30 bytes   delete    str1     Possible access violation  What a disaster    4  Be careful with local pointers  A pointer you declare in a function is allocated on the stack  but the dynamic variable it points to is allocated on the heap  If you don t delete it  it will persist after the program exits from the function   void Leak int x    char  p   new char  x       delete    p     Remove the first comment marking to correct       5  Pay attention to the square braces after  delete   Use delete by itself to free a single object  Use delete    with square brackets to free a heap array  Don t do something like this   char  one   new char   delete    one     Wrong  char  many   new char  30    delete many     Wrong    6  If the leak yet allowed - I m usually seeking it with deleaker  check it here  http   deleaker com

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Neither  new  or  delete  should ever be used in application code  Instead  create a new type that uses the manager worker idiom  in which the manager class allocates and frees memory and forwards all other operations to the worker object   Unfortunately this is more work than it should be because C   doesn t have overloading of  operator     It is even more work in the presence of polymorphism   But this is worth the effort because you then don t ever have to worry about memory leaks  which means you don t even have to look for them

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MTuner is a free multi platform memory profiling  leak detection and analysis tool supporting MSVC  GCC and Clang compilers  Features include     timeline based history of memory usage and live memory blocks powerful memory operation filtering based on heap  memory tag  time range  etc  SDK for manual instrumentation with full source code continuous integration support through command line usage call stack tree and tree map navigation much more     Users can profile any software targeting platforms with GCC or Clang cross compilers  MTuner comes with built in support for Windows  PlayStation 4 and PlayStation 3 platforms

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A survey of automatic memory leak checkers  In this answer  I compare several different memory leak checkers in a simple easy to understand memory leak example   Before anything  see this huge table in the ASan wiki which compares all tools known to man  https   github com google sanitizers wiki AddressSanitizerComparisonOfMemoryTools d06210f759fec97066888e5f27c7e722832b0924  The example analyzed will be   main c   include  lt stdlib h gt   void   my malloc size t n        return malloc n      void leaky size t n  int do leak        void  p   my malloc n       if   do leak            free p            int main void        leaky 0x10  0       leaky 0x10  1       leaky 0x100  0       leaky 0x100  1       leaky 0x1000  0       leaky 0x1000  1       GitHub upstream   We will try to see how clearly do the different tools point us to the leaky calls   tcmalloc from gperftools by Google  https   github com gperftools gperftools  Usage on Ubuntu 19 04   sudo apt-get install google-perftools gcc -ggdb3 -o main out main c -ltcmalloc PPROF PATH  usr bin google-pprof     HEAPCHECK normal     HEAPPROFILE ble       main out     google-pprof main out ble 0001 heap --text   The output of the program run contains the memory leak analysis   WARNING  Perftools heap leak checker is active -- Performance may suffer Starting tracking the heap Dumping heap profile to ble 0001 heap  Exiting  4 kB in use  Have memory regions w o callers  might report false leaks Leak check  main  detected leaks of 272 bytes in 2 objects The 2 largest leaks  Using local file   main out  Leak of 256 bytes in 1 objects allocated from            555bf6e5815d my malloc           555bf6e5817a leaky           555bf6e581d3 main           7f71e88c9b6b   libc start main           555bf6e5808a  start Leak of 16 bytes in 1 objects allocated from            555bf6e5815d my malloc           555bf6e5817a leaky           555bf6e581b5 main           7f71e88c9b6b   libc start main           555bf6e5808a  start   If the preceding stack traces are not enough to find the leaks  try running THIS shell command   pprof   main out   tmp main out 24744  main -end heap  --inuse objects --lines --heapcheck  --edgefraction 1e-10 --nodefraction 1e-10 --gv  If you are still puzzled about why the leaks are there  try rerunning this program with HEAP CHECK TEST POINTER ALIGNMENT 1 and or with HEAP CHECK MAX POINTER OFFSET -1 If the leak report occurs in a small fraction of runs  try running with TCMALLOC MAX FREE QUEUE SIZE of few hundred MB or with TCMALLOC RECLAIM MEMORY false  it might help find leaks more re Exiting with error code  instead of crashing  because of whole-program memory leaks   and the output of google-pprof contains the heap usage analysis   Using local file main out  Using local file ble 0001 heap  Total  0 0 MB      0 0 100 0  100 0       0 0 100 0  my malloc      0 0   0 0  100 0       0 0 100 0    libc start main      0 0   0 0  100 0       0 0 100 0   start      0 0   0 0  100 0       0 0 100 0  leaky      0 0   0 0  100 0       0 0 100 0  main   The output points us to two of the three leaks   Leak of 256 bytes in 1 objects allocated from            555bf6e5815d my malloc           555bf6e5817a leaky           555bf6e581d3 main           7f71e88c9b6b   libc start main           555bf6e5808a  start Leak of 16 bytes in 1 objects allocated from            555bf6e5815d my malloc           555bf6e5817a leaky           555bf6e581b5 main           7f71e88c9b6b   libc start main           555bf6e5808a  start   I m not sure why the third one didn t show up  In any case  when usually when something leaks  it happens a lot of times  and when I used it on a real project  I just ended up being pointed out to the leaking function very easily   As mentioned on the output itself  this incurs a significant execution slowdown   Further documentation at    https   gperftools github io gperftools heap checker html https   gperftools github io gperftools heapprofile html   See also  How To Use TCMalloc   Tested in Ubuntu 19 04  google-perftools 2 5-2   Address Sanitizer  ASan  also by Google  https   github com google sanitizers  Previously mentioned at  How to find memory leak in a C   code project  TODO vs tcmalloc   This is already integrated into GCC  so you can just do   gcc -fsanitize address -ggdb3 -o main out main c   main out    and execution outputs                                                                       27223  ERROR  LeakSanitizer  detected memory leaks  Direct leak of 4096 byte s  in 1 object s  allocated from       0 0x7fabbefc5448 in malloc   usr lib x86 64-linux-gnu libasan so 5 0x10c448       1 0x55bf86c5f17c in my malloc  home ciro test main c 4      2 0x55bf86c5f199 in leaky  home ciro test main c 8      3 0x55bf86c5f210 in main  home ciro test main c 20      4 0x7fabbecf4b6a in   libc start main   lib x86 64-linux-gnu libc so 6 0x26b6a   Direct leak of 256 byte s  in 1 object s  allocated from       0 0x7fabbefc5448 in malloc   usr lib x86 64-linux-gnu libasan so 5 0x10c448       1 0x55bf86c5f17c in my malloc  home ciro test main c 4      2 0x55bf86c5f199 in leaky  home ciro test main c 8      3 0x55bf86c5f1f2 in main  home ciro test main c 18      4 0x7fabbecf4b6a in   libc start main   lib x86 64-linux-gnu libc so 6 0x26b6a   Direct leak of 16 byte s  in 1 object s  allocated from       0 0x7fabbefc5448 in malloc   usr lib x86 64-linux-gnu libasan so 5 0x10c448       1 0x55bf86c5f17c in my malloc  home ciro test main c 4      2 0x55bf86c5f199 in leaky  home ciro test main c 8      3 0x55bf86c5f1d4 in main  home ciro test main c 16      4 0x7fabbecf4b6a in   libc start main   lib x86 64-linux-gnu libc so 6 0x26b6a   SUMMARY  AddressSanitizer  4368 byte s  leaked in 3 allocation s     which clearly identifies all leaks  Nice   ASan can also do other cool checks such as out-of-bounds writes  Stack smashing detected  Tested in Ubuntu 19 04  GCC 8 3 0   Valgrind  http   www valgrind org   Previously mentioned at  https   stackoverflow com a 37661630 895245  Usage   sudo apt-get install valgrind gcc -ggdb3 -o main out main c valgrind --leak-check yes   main out   Output     32178   Memcheck  a memory error detector   32178   Copyright  C  2002-2017  and GNU GPL d  by Julian Seward et al    32178   Using Valgrind-3 14 0 and LibVEX  rerun with -h for copyright info   32178   Command    main out   32178      32178      32178   HEAP SUMMARY    32178       in use at exit  4 368 bytes in 3 blocks   32178     total heap usage  6 allocs  3 frees  8 736 bytes allocated   32178      32178   16 bytes in 1 blocks are definitely lost in loss record 1 of 3   32178      at 0x483874F  malloc  in  usr lib x86 64-linux-gnu valgrind vgpreload memcheck-amd64-linux so    32178      by 0x10915C  my malloc  main c 4    32178      by 0x109179  leaky  main c 8    32178      by 0x1091B4  main  main c 16    32178      32178   256 bytes in 1 blocks are definitely lost in loss record 2 of 3   32178      at 0x483874F  malloc  in  usr lib x86 64-linux-gnu valgrind vgpreload memcheck-amd64-linux so    32178      by 0x10915C  my malloc  main c 4    32178      by 0x109179  leaky  main c 8    32178      by 0x1091D2  main  main c 18    32178      32178   4 096 bytes in 1 blocks are definitely lost in loss record 3 of 3   32178      at 0x483874F  malloc  in  usr lib x86 64-linux-gnu valgrind vgpreload memcheck-amd64-linux so    32178      by 0x10915C  my malloc  main c 4    32178      by 0x109179  leaky  main c 8    32178      by 0x1091F0  main  main c 20    32178      32178   LEAK SUMMARY    32178      definitely lost  4 368 bytes in 3 blocks   32178      indirectly lost  0 bytes in 0 blocks   32178        possibly lost  0 bytes in 0 blocks   32178      still reachable  0 bytes in 0 blocks   32178           suppressed  0 bytes in 0 blocks   32178      32178   For counts of detected and suppressed errors  rerun with  -v   32178   ERROR SUMMARY  3 errors from 3 contexts  suppressed  0 from 0    So once again  all leaks were detected   See also  How do I use valgrind to find memory leaks   Tested in Ubuntu 19 04  valgrind 3 14 0

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On Windows you can use CRT debug heap      Is there any standard or procedure one should follow to ensure there is no memory leak in the program    Yeah  don t use manual memory management  if you ever call delete or delete   manually  then you re doing it wrong   Use RAII and smart pointers  limit heap allocations to the absolute minimum  most of the time  automatic variables will suffice

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Valgrind http   valgrind org   and   GDB http   www gnu org software gdb

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In visual studio  there is a built in detector for memory leak called C Runtime Library  When your program exits after the main function returns  CRT will check the debug heap of your application  if you have any blocks still allocated on the debug heap  then you have memory leak   This forum discusses a few ways to avoid memory leakage in C C

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Running  Valgrind  can   1  Help Identify Memory Leaks - show you how many memory leaks you have  and point out to the lines in the code where the leaked memory was allocated   2  Point out wrong attempts to free memory  e g  improper call of delete   Instructions for using  Valgrind   1  Get valgrind here   2  Compile your code with -g flag  3  In your shell run   valgrind --leak-check yes myprog arg1 arg2   Where  myprog  is your compiled program and arg1  arg2 your programme s arguments   4  The result is a list of calls to malloc new that did not have subsequent calls to free delete   For example     4230      at 0x1B977DD0  malloc  vg replace malloc c 136     4230      by 0x804990F  main  example c 6    Tells you in which line the malloc  that was not freed  was called   As Pointed out by others  make sure that for every new malloc call  you have a subsequent delete free call

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There are some well-known programming techniques that will help you to minimize the risk of getting memory leaks at first hand    if you have to do your own dynamic memory allocation  write new and delete always pairwise  and make sure the allocation deallocation code is called pairwise avoid dynamic memory allocation if you can  For example  use vector lt T gt  t whereever possible instead of T  t   new T size  use  smart pointers  like boost smart pointers  http   www boost org doc libs 1 46 1 libs smart ptr smart ptr htm  my personal favorite  make sure you have understood the concept of ownership of a pointer  and make sure that everywhere where you use pointers  you know which code entity is the owner learn which constructors   assignment operators are automatically created by the C   compiler  and what that means if you have class that owns a pointer  or what that means if you have a class that contains a pointer to an object it does not own

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You can use the tool Valgrind to detect memory leaks   Also  to find the leak in a particular function  use exit 0  at the end of the function and then run it with Valgrind      valgrind   your CPP program

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If you use gcc  there s gprof available      I wanted to the know how programmer find memory leak   Some uses tools  some does what you do  could also through peer code review     Is there any standard or procedure one should follow to ensure there is no memory leak in the program   For me  whenever I create dynamically allocated objects  I always put the freeing code after  then fill the code between  This would be OK if you re sure there won t be exceptions in the code between  Otherwise  I make use of try-finally  I don t use C   frequently

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In addition to the tools and methodes provided in the other anwers  static code analysis tools can be used to detect memory leaks  and other issues as well   A free an robust tool is Cppcheck  But there are a lot of other tools available  Wikipedia has a list of static code analysis tools

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Search your code for occurrences of new  and make sure that they all occur within a constructor with a matching delete in a destructor  Make sure that this is the only possibly throwing operation in that constructor  A simple way to do this is to wrap all pointers in std  auto ptr  or boost  scoped ptr  depending on whether or not you need move semantics   For all future code just ensure that every resource is owned by an object that cleans up the resource in its destructor  If you need move semantics then you can upgrade to a compiler that supports r-value references  VS2010 does I believe  and create move constructors  If you don t want to do that then you can use a variety of tricky techniques involving conscientious usage of swap  or try the Boost Move library

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Make certain that all the heap memory is successfully freed  There is no need if you never allocate memory on the heap  If you do  count the number of times you malloc memory  and count up the number of time you free memory

[c++] How to find memory leak in a C++ code/project?

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