How to get memory usage at runtime using C

Question

I need to get the mem usage VIRT and RES at run time of my program and display them   What i tried so far   getrusage  http   linux die net man 2 getrusage   int who   RUSAGE SELF   struct rusage usage   int ret    ret getrusage who  amp usage    cout lt  lt usage ru maxrss    but i always get 0

User · Answer

The existing answers are better for how to get the correct value, but I can at least explain why getrusage isn't working for you.

man 2 getrusage:

The above struct [rusage] was taken from BSD 4.3 Reno. Not all fields are meaningful under Linux. Right now (Linux 2.4, 2.6) only the fields ru_utime, ru_stime, ru_minflt, ru_majflt, and ru_nswap are maintained.

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On linux  if you can afford the run time cost  for debugging   you can use valgrind with the massif tool   http   valgrind org docs manual ms-manual html  It is heavy weight  but very useful

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A more elegant way for Don Wakefield method    include  lt iostream gt   include  lt fstream gt   using namespace std   int main         int tSize   0  resident   0  share   0      ifstream buffer   proc self statm        buffer  gt  gt  tSize  gt  gt  resident  gt  gt  share      buffer close         long page size kb   sysconf  SC PAGE SIZE    1024     in case x86-64 is configured to use 2MB pages     double rss   resident   page size kb      cout  lt  lt   RSS -    lt  lt  rss  lt  lt    kB n        double shared mem   share   page size kb      cout  lt  lt   Shared Memory -    lt  lt  shared mem  lt  lt    kB n        cout  lt  lt   Private Memory -    lt  lt  rss - shared mem  lt  lt   kB n       return 0

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Old      maxrss states the maximum available   memory for the process  0 means that   no limit is put upon the process  What   you probably want is unshared data   usage ru idrss    New  It seems that the above does not actually work  as the kernel does not fill most of the values  What does work is to get the information from proc  Instead of parsing it oneself though  it is easier to use libproc  part of procps  as follows      getrusage c  include  lt stdio h gt   include  lt proc readproc h gt   int main       struct proc t usage    look up our self  amp usage     printf  usage   lu n   usage vsize       Compile with  gcc -o getrusage getrusage c -lproc

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David Robert Nadeau has put a good self contained multi-platform C function to get the process resident set size  physical memory use  in his website         Author   David Robert Nadeau    Site     http   NadeauSoftware com     License  Creative Commons Attribution 3 0 Unported License             http   creativecommons org licenses by 3 0 deed en US       if defined  WIN32   include  lt windows h gt   include  lt psapi h gt    elif defined   unix       defined   unix     defined unix      defined   APPLE     amp  amp  defined   MACH      include  lt unistd h gt   include  lt sys resource h gt    if defined   APPLE     amp  amp  defined   MACH     include  lt mach mach h gt    elif  defined  AIX     defined   TOS  AIX         defined   sun       defined   sun     defined sun   amp  amp   defined   SVR4     defined   svr4       include  lt fcntl h gt   include  lt procfs h gt    elif defined   linux       defined   linux     defined linux     defined   gnu linux     include  lt stdio h gt    endif   else  error  Cannot define getPeakRSS    or getCurrentRSS    for an unknown OS    endif             Returns the peak  maximum so far  resident set size  physical    memory use  measured in bytes  or zero if the value cannot be    determined on this OS      size t getPeakRSS       if defined  WIN32         Windows --------------------------------------------------        PROCESS MEMORY COUNTERS info      GetProcessMemoryInfo  GetCurrentProcess      amp info  sizeof info         return  size t info PeakWorkingSetSize    elif  defined  AIX     defined   TOS  AIX         defined   sun       defined   sun     defined sun   amp  amp   defined   SVR4     defined   svr4             AIX and Solaris ------------------------------------------        struct psinfo psinfo      int fd   -1      if    fd   open    proc self psinfo   O RDONLY       -1           return  size t 0L          Can t open         if   read  fd   amp psinfo  sizeof psinfo       sizeof psinfo                  close  fd            return  size t 0L          Can t read               close  fd        return  size t  psinfo pr rssize   1024L     elif defined   unix       defined   unix     defined unix      defined   APPLE     amp  amp  defined   MACH            BSD  Linux  and OSX --------------------------------------        struct rusage rusage      getrusage  RUSAGE SELF   amp rusage     if defined   APPLE     amp  amp  defined   MACH        return  size t rusage ru maxrss   else     return  size t  rusage ru maxrss   1024L    endif   else        Unknown OS -----------------------------------------------        return  size t 0L              Unsupported      endif               Returns the current resident set size  physical memory use  measured    in bytes  or zero if the value cannot be determined on this OS      size t getCurrentRSS       if defined  WIN32         Windows --------------------------------------------------        PROCESS MEMORY COUNTERS info      GetProcessMemoryInfo  GetCurrentProcess      amp info  sizeof info         return  size t info WorkingSetSize    elif defined   APPLE     amp  amp  defined   MACH           OSX ------------------------------------------------------        struct mach task basic info info      mach msg type number t infoCount   MACH TASK BASIC INFO COUNT      if   task info  mach task self     MACH TASK BASIC INFO           task info t  amp info   amp infoCount      KERN SUCCESS           return  size t 0L          Can t access         return  size t info resident size    elif defined   linux       defined   linux     defined linux     defined   gnu linux           Linux ----------------------------------------------------        long rss   0L      FILE  fp   NULL      if    fp   fopen    proc self statm    r        NULL           return  size t 0L          Can t open         if   fscanf  fp     s ld    amp rss      1                 fclose  fp            return  size t 0L          Can t read               fclose  fp        return  size t rss    size t sysconf   SC PAGESIZE     else        AIX  BSD  Solaris  and Unknown OS ------------------------        return  size t 0L              Unsupported      endif     Usage  size t currentSize   getCurrentRSS     size t peakSize      getPeakRSS       For more discussion  check the web site  it also provides a function to get the physical memory size of a system

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Based on Don W s solution  with fewer variables   void process mem usage double amp  vm usage  double amp  resident set        vm usage       0 0      resident set   0 0          the two fields we want     unsigned long vsize      long rss                std  string ignore          std  ifstream ifs   proc self stat   std  ios base  in           ifs  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore                  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore  gt  gt  ignore                  gt  gt  ignore  gt  gt  ignore  gt  gt  vsize  gt  gt  rss             long page size kb   sysconf  SC PAGE SIZE    1024     in case x86-64 is configured to use 2MB pages     vm usage   vsize   1024 0      resident set   rss   page size kb

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On your system there is a file named  proc self statm  The proc filesystem is a pseudo-filesystem which provides an interface to kernel data structures  This file contains the information you need in columns with only integers that are space separated   Column no       total program size  VmSize in  proc  pid  status    resident set size   VmRSS in  proc  pid  status    For more info see the LINK

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in additional to your way you could call system ps command and get memory usage from it output  or read info from  proc pid    see PIOCPSINFO struct

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On Linux  I ve never found an ioctl   solution  For our applications  we coded a general utility routine based on reading files in  proc pid  There are a number of these files which give differing results  Here s the one we settled on  the question was tagged C    and we handled I O using C   constructs  but it should be easily adaptable to C i o routines if you need to     include  lt unistd h gt   include  lt ios gt   include  lt iostream gt   include  lt fstream gt   include  lt string gt                                                                                        process mem usage double  amp   double  amp   - takes two doubles by reference     attempts to read the system-dependent data for a process  virtual memory    size and resident set size  and return the results in KB        On failure  returns 0 0  0 0  void process mem usage double amp  vm usage  double amp  resident set       using std  ios base     using std  ifstream     using std  string      vm usage       0 0     resident set   0 0          file  stat seems to give the most reliable results          ifstream stat stream   proc self stat  ios base  in          dummy vars for leading entries in stat that we don t care about          string pid  comm  state  ppid  pgrp  session  tty nr     string tpgid  flags  minflt  cminflt  majflt  cmajflt     string utime  stime  cutime  cstime  priority  nice     string O  itrealvalue  starttime         the two fields we want          unsigned long vsize     long rss      stat stream  gt  gt  pid  gt  gt  comm  gt  gt  state  gt  gt  ppid  gt  gt  pgrp  gt  gt  session  gt  gt  tty nr                 gt  gt  tpgid  gt  gt  flags  gt  gt  minflt  gt  gt  cminflt  gt  gt  majflt  gt  gt  cmajflt                 gt  gt  utime  gt  gt  stime  gt  gt  cutime  gt  gt  cstime  gt  gt  priority  gt  gt  nice                 gt  gt  O  gt  gt  itrealvalue  gt  gt  starttime  gt  gt  vsize  gt  gt  rss     don t care about the rest     stat stream close        long page size kb   sysconf  SC PAGE SIZE    1024     in case x86-64 is configured to use 2MB pages    vm usage       vsize   1024 0     resident set   rss   page size kb     int main        using std  cout     using std  endl      double vm  rss     process mem usage vm  rss      cout  lt  lt   VM     lt  lt  vm  lt  lt     RSS     lt  lt  rss  lt  lt  endl

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I am using other way to do that and it sounds realistic  What I do is i got the PID of the process by getpid   function and then I use  proc pid stat file  I believe the 23rd column of the stat file is the vmsize  look at the Don post   You may read the vmsize from the file wherever you need in the code  In case you wonder how much a snippet of a code may use memory  you may read that file once before that snippet and once after and you can subtract them from each other

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I was looking for a Linux app to measure maximum memory used  valgrind is an excellent tool  but was giving me more information than I wanted  tstime seemed to be the best tool I could find  It measures  highwater  memory usage  RSS and virtual   See this answer

[c++] How to get memory usage at runtime using C++?

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