Measuring time in C and linux

I want to see how much is done by the C program, so I wrote:


  int (*deallocate_ptr)(memContainer *,void*);

  void (*merge_ptr)(node *);

  void* (*allocate_ptr)(memContainer *,unsigned long size);

  memContainer* (*init_ptr)(unsigned long );

  diagStruct* (*diagnose_ptr)(memContainer *);

  void (*finalize_ptr)(memContainer *);

  void (*printNode_ptr)(node *n);

  void (*printContainer_ptr)(memContainer *c);

  void info(memContainer *c)
    struct tms *t;
    t=malloc(sizeof(struct tms));
    printf("user : %d\nsystem : %d\n %d",t->tms_utime,(int)t->tms_stime);
    return ;


but when i call this function i get 0 user time and 0 system time, even if i write:

for (i=0;i<100000;++i)
    for (j=0;j<10;++j)


what am I doing wrong?


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3 answers

Below is a demo program that outputs a non-zero time:

#include <iostream>
using namespace std;

int main()
    int x = 0;
    for (int i = 0; i < 1 << 30; i++)

    struct tms t;
    cout << t.tms_utime << endl;
    cout << t.tms_stime << endl;
    return x;







The compiler is probably optimizing your loops for

as they don't do anything. Try increasing the variable volatile


If you want to know the time, try running time ./app

and it will output the current cputime, wall clock, etc. the executed application.



The code could just write the variable volatile

at the beginning, put its work in a function (in a separate file), then read volatile

after the "work" and print something including volatile


Or, do a simple calculation with the calculation part buried in a function, or using the return function.

What platform (operating system and compiler) are you using?

I don't know what platform you are on, but there are some helpful stackoverflow questions about high precision system clock. High fidelity user space synchronization in Linux contains several useful links and references.

Synchronization techniques in C ++ under Linux looked useful.



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