如何从 C++ 程序内部测量内存使用情况？

Question

Is it possible, for a c++ program, to track how much memory the program is using at one time?

For example, a function with a prototype:

int getEstimatedTotalMemoryUsage();

I suppose if it's not possible, then one will have to get out of the program, do a system call and check the results from there. If so, what tools are available for such purposes? Assuming such a thing is possible, that is.

edit: I'm using linux, any tools that can do this for you?

Answer 1

Yes - use POSIX getrusage . From the Linux man page :

Synopsis

#include <sys/time.h> #include <sys/resource.h> int getrusage(int who, struct rusage *usage);

Description

getrusage() returns current resource usages, for a who of either RUSAGE_SELF or RUSAGE_CHILDREN . The former asks for resources used by the current process, the latter for resources used by those of its children that have terminated and have been waited for.

 struct rusage { struct timeval ru_utime; /* user time used */ struct timeval ru_stime; /* system time used */ long ru_maxrss; /* maximum resident set size */ long ru_ixrss; /* integral shared memory size */ long ru_idrss; /* integral unshared data size */ long ru_isrss; /* integral unshared stack size */ long ru_minflt; /* page reclaims */ long ru_majflt; /* page faults */ long ru_nswap; /* swaps */ long ru_inblock; /* block input operations */ long ru_oublock; /* block output operations */ long ru_msgsnd; /* messages sent */ long ru_msgrcv; /* messages received */ long ru_nsignals; /* signals received */ long ru_nvcsw; /* voluntary context switches */ long ru_nivcsw; /* involuntary context switches */ };

Answer 2

Here is an example of measuring memory used by process on Windows.

#include <windows.h>
#include <Psapi.h>

// [...]

PROCESS_MEMORY_COUNTERS memCounter;
BOOL result = K32GetProcessMemoryInfo(GetCurrentProcess(), &memCounter, sizeof(memCounter));
std::cout << "WorkingSetSize " << memCounter.WorkingSetSize << std::endl;

And explanations of returned values https://docs.microsoft.com/en-gb/windows/win32/api/psapi/ns-psapi-process_memory_counters

Answer 3

I wanted this today, myself, so sharing the tested results here. I believe a call to getmem() will do what the OP asked, on any unix box. Written in very generic C, it will work in C or C++.

// Calling function must free the returned result.
char* exec(const char* command) {
  FILE* fp;
  char* line = NULL;
  // Following initialization is equivalent to char* result = ""; and just
  // initializes result to an empty string, only it works with
  // -Werror=write-strings and is so much less clear.
  char* result = (char*) calloc(1, 1);
  size_t len = 0;

  fflush(NULL);
  fp = popen(command, "r");
  if (fp == NULL) {
    printf("Cannot execute command:\n%s\n", command);
    return NULL;
  }

  while(getline(&line, &len, fp) != -1) {
    // +1 below to allow room for null terminator.
    result = (char*) realloc(result, strlen(result) + strlen(line) + 1);
    // +1 below so we copy the final null terminator.
    strncpy(result + strlen(result), line, strlen(line) + 1);
    free(line);
    line = NULL;
  }

  fflush(fp);
  if (pclose(fp) != 0) {
    perror("Cannot close stream.\n");
  }
  return result;
}

int getmem() {
  pid_t pid = getpid();
  char cmd[64];
  snprintf(cmd, 64, "/bin/ps -p %d -o size", pid);
  char* result = exec(cmd);
  if (!result) {
    return 0;
  }
  // Find first newline.
  int pos = 0;
  while (result[pos] != '\n') {
    pos++;
  }
  // Remove the final newline.
  result[strlen(result) - 1] = '\0';
  // Convert to integer.
  int size = atoi(result + pos + 1);
  free(result);
  return size;
}

Technically, I suppose the printf(...) line should be fprintf(stderr, ...), but I tend to have stderr redirected for certain environment-specific logging reasons, and this is how I compiled and tested the code, so I'm copying verbatim to avoid breakage.

Answer 4

Get your PID: pid_t getpid(void); // unistd.h pid_t getpid(void); // unistd.h

Parse /proc/<id>/smaps

If you don't care about shared libraries in mem total it may be simpler

make a system call to ps -p <id> -o %mem