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运维监控程序中经常需要根据一个进程号pid去监控实时的cpu和内存占用，以下整理了一个C++实现的简单例子，并封装为方便跨平台调用的函数

代码

#include <iostream>
#include <thread>
#include <chrono>
#include <string.h>#ifdef WIN32
#include <windows.h>  
#include <psapi.h>  
//#include <tlhelp32.h>
#include <direct.h>
#include <process.h>
#else
#include <sys/stat.h>
#include <sys/sysinfo.h>
#include <sys/time.h>
#include <unistd.h>
#endif// get current process pid
inline int GetCurrentPid()
{return getpid();
}// get specific process cpu occupation ratio by pid
#ifdef WIN32
// 
static uint64_t convert_time_format(const FILETIME* ftime)
{LARGE_INTEGER li;li.LowPart = ftime->dwLowDateTime;li.HighPart = ftime->dwHighDateTime;return li.QuadPart;
}
#else
// FIXME: can also get cpu and mem status from popen cmd
// the info line num in /proc/{pid}/status file
#define VMRSS_LINE 22
#define PROCESS_ITEM 14static const char* get_items(const char* buffer, unsigned int item)
{// read from buffer by offsetconst char* p = buffer;int len = strlen(buffer);int count = 0;for (int i = 0; i < len; i++){if (' ' == *p){count++;if (count == item - 1){p++;break;}}p++;}return p;
}static inline unsigned long get_cpu_total_occupy()
{// get total cpu use time// different mode cpu occupy timeunsigned long user_time;unsigned long nice_time;unsigned long system_time;unsigned long idle_time;FILE* fd;char buff[1024] = { 0 };fd = fopen("/proc/stat", "r");if (nullptr == fd)return 0;fgets(buff, sizeof(buff), fd);char name[64] = { 0 };sscanf(buff, "%s %ld %ld %ld %ld", name, &user_time, &nice_time, &system_time, &idle_time);fclose(fd);return (user_time + nice_time + system_time + idle_time);
}static inline unsigned long get_cpu_proc_occupy(int pid)
{// get specific pid cpu use timeunsigned int tmp_pid;unsigned long utime;  // user timeunsigned long stime;  // kernel timeunsigned long cutime; // all user timeunsigned long cstime; // all dead timechar file_name[64] = { 0 };FILE* fd;char line_buff[1024] = { 0 };sprintf(file_name, "/proc/%d/stat", pid);fd = fopen(file_name, "r");if (nullptr == fd)return 0;fgets(line_buff, sizeof(line_buff), fd);sscanf(line_buff, "%u", &tmp_pid);const char* q = get_items(line_buff, PROCESS_ITEM);sscanf(q, "%ld %ld %ld %ld", &utime, &stime, &cutime, &cstime);fclose(fd);return (utime + stime + cutime + cstime);
}
#endifinline float GetCpuUsageRatio(int pid)
{
#ifdef WIN32static int64_t last_time = 0;static int64_t last_system_time = 0;FILETIME now;FILETIME creation_time;FILETIME exit_time;FILETIME kernel_time;FILETIME user_time;int64_t system_time;int64_t time;int64_t system_time_delta;int64_t time_delta;// get cpu numSYSTEM_INFO info;GetSystemInfo(&info);int cpu_num = info.dwNumberOfProcessors;float cpu_ratio = 0.0;// get process hanlde by pidHANDLE process = OpenProcess(PROCESS_ALL_ACCESS, FALSE, pid);// use GetCurrentProcess() can get current process and no need to close handle// get now timeGetSystemTimeAsFileTime(&now);if (!GetProcessTimes(process, &creation_time, &exit_time, &kernel_time, &user_time)){// We don't assert here because in some cases (such as in the Task Manager)  // we may call this function on a process that has just exited but we have  // not yet received the notification.  printf("GetCpuUsageRatio GetProcessTimes failed\n");return 0.0;}// should handle the multiple cpu numsystem_time = (convert_time_format(&kernel_time) + convert_time_format(&user_time)) / cpu_num;time = convert_time_format(&now);if ((last_system_time == 0) || (last_time == 0)){// First call, just set the last values.  last_system_time = system_time;last_time = time;return 0.0;}system_time_delta = system_time - last_system_time;time_delta = time - last_time;CloseHandle(process);if (time_delta == 0){printf("GetCpuUsageRatio time_delta is 0, error\n");return 0.0;}// We add time_delta / 2 so the result is rounded.  cpu_ratio = (int)((system_time_delta * 100 + time_delta / 2) / time_delta); // the % unitlast_system_time = system_time;last_time = time;cpu_ratio /= 100.0; // convert to float numberreturn cpu_ratio;
#elseunsigned long totalcputime1, totalcputime2;unsigned long procputime1, procputime2;totalcputime1 = get_cpu_total_occupy();procputime1 = get_cpu_proc_occupy(pid);// FIXME: the 200ms is a magic number, works wellusleep(200000); // sleep 200ms to fetch two time point cpu usage snapshots sample for later calculationtotalcputime2 = get_cpu_total_occupy();procputime2 = get_cpu_proc_occupy(pid);float pcpu = 0.0;if (0 != totalcputime2 - totalcputime1)pcpu = (procputime2 - procputime1) / float(totalcputime2 - totalcputime1); // float numberint cpu_num = get_nprocs();pcpu *= cpu_num; // should multiply cpu num in multiple cpu machinereturn pcpu;
#endif
}// get specific process physical memeory occupation size by pid (MB)
inline float GetMemoryUsage(int pid)
{
#ifdef WIN32uint64_t mem = 0, vmem = 0;PROCESS_MEMORY_COUNTERS pmc;// get process hanlde by pidHANDLE process = OpenProcess(PROCESS_ALL_ACCESS, FALSE, pid);if (GetProcessMemoryInfo(process, &pmc, sizeof(pmc))){mem = pmc.WorkingSetSize;vmem = pmc.PagefileUsage;}CloseHandle(process);// use GetCurrentProcess() can get current process and no need to close handle// convert mem from B to MBreturn mem / 1024.0 / 1024.0;#elsechar file_name[64] = { 0 };FILE* fd;char line_buff[512] = { 0 };sprintf(file_name, "/proc/%d/status", pid);fd = fopen(file_name, "r");if (nullptr == fd)return 0;char name[64];int vmrss = 0;for (int i = 0; i < VMRSS_LINE - 1; i++)fgets(line_buff, sizeof(line_buff), fd);fgets(line_buff, sizeof(line_buff), fd);sscanf(line_buff, "%s %d", name, &vmrss);fclose(fd);// cnvert VmRSS from KB to MBreturn vmrss / 1024.0;
#endif
}int main()
{// launch some task to occupy cpu and memoryfor (int i = 0; i < 5; i++)std::thread([]{std::this_thread::sleep_for(std::chrono::milliseconds(10));}).detach();int current_pid = GetCurrentPid(); // or you can set a outside program pidfloat cpu_usage_ratio = GetCpuUsageRatio(current_pid);float memory_usage = GetMemoryUsage(current_pid);while (true){std::cout << "current pid: " << current_pid << std::endl;std::cout << "cpu usage ratio: " << cpu_usage_ratio * 100 << "%" << std::endl;std::cout << "memory usage: " << memory_usage << "MB" << std::endl;std::this_thread::sleep_for(std::chrono::milliseconds(1000));}return 0;
}

运行结果

current pid: 17258
cpu usage ratio: 114.286%
memory usage: 8889.9MB

直接使用GetCpuUsageRatio和GetMemoryUsage就行了，有几个说明

• linux下其实是通过读取并解析/proc目录下进程虚拟文件对应字段值计算得到
• windows下调用系统api计算得到
• 这种打点采样获取cpu和内存占用的方式数据跟用系统管理器查看到的不完全一致