Question

My code is the following:

#include <iostream>
#include <sys/time.h>
using namespace std;

int main(int argc, char** argv) {
                if(argv[0])
                        argc++;

                struct timeval m_timeEnd, m_timeCreate, m_timeStart;
        long mtime, alltime, seconds, useconds;

                gettimeofday(&m_timeStart,NULL);
                sleep(3);
                gettimeofday(&m_timeCreate,NULL);
                sleep(1);

        gettimeofday(&m_timeEnd, NULL);
        seconds  = m_timeEnd.tv_sec  - m_timeStart.tv_sec;
        useconds = m_timeEnd.tv_usec - m_timeStart.tv_usec;

        mtime = (long) (((seconds) * 1000 + useconds/1000.0) + 0.5);
        seconds = useconds = 0;
        seconds  = m_timeEnd.tv_sec  - m_timeCreate.tv_sec;
        useconds = m_timeEnd.tv_usec - m_timeCreate.tv_usec;
        alltime = (long) (((seconds) * 1000 + useconds/1000.0) + 0.5);

        printf("IN=%ld ALL=%ld milsec.\n", mtime, alltime);

}

I am compiling with

g++ -W -Wall -Wno-unknown-pragmas -Wpointer-arith -Wcast-align
-Wcast-qual -Wsign-compare -Wconversion -O -fno-strict-aliasing

and I have some warnings that I need to eliminate. How?

a1.cpp:21: warning: conversion to 'double' from 'long int' may alter its value
a1.cpp:21: warning: conversion to 'double' from 'long int' may alter its value
a1.cpp:25: warning: conversion to 'double' from 'long int' may alter its value
a1.cpp:25: warning: conversion to 'double' from 'long int' may alter its value

Answer 1

This should work:

mtime = (long)(((long long)seconds*1000000 + useconds + 500)/1000);

Convert the expression for alltime in the same way.

The reason you see the warnings is that your expression converts from long to double and back to do the math. You can avoid it by re-shuffling your expressions a bit to stay entirely within integral types. Note the conversion to long long to avoid overflowing (thanks, Nick).

EDIT You can further simplify this and eliminate the conversion:

mtime = seconds*1000 + (useconds + 500)/1000;