CODEWITHSUNDEEP
c
user3593148
user3593148

Reputation: 505

How to include clock_gettime in a c make file

I know that in order to use the clock_gettime(2) function, you have to include -lrt in the makefile but I have no idea where it goes. Where would I put it in the example makefile.

CFLAGS = -g -Wall -std=c99
CC = gcc

objects = example.o

example: $(objects)
    $(CC) $(CFLAGS) -o example $(objects)

example.o: example.c
    $(CC) $(CFLAGS) -c example.c
clean:
    rm test $(objects)

Edit: how my lrt looks.

enter image description here

enter image description here

What my code is:

#include "stdio.h"
#include "stdlib.h"
#include <time.h>

int main(int argc, char *argv[]) {

    struct timespec starttime, endtime;
    double elapsed;
    clock_gettime(CLOCK_REALTIME, &starttime);

    /// work to be timed

    clock_gettime(CLOCK_REALTIME, &endtime);
    elapsed = ((endtime.tv_sec-starttime.tv_sec)*1000000000.0 + (endtime.tv_nsec - starttime.tv_nsec))/1000000000;
    // elapsed time can also be calculated as
    if (endtime.tv_nsec < starttime.tv_nsec) {
        // borrow a second
        elapsed = (endtime.tv_sec - starttime.tv_sec - 1) + (1000000000.0 + endtime.tv_nsec - starttime.tv_nsec)/1000000000;
    }
    else {
        elapsed = (endtime.tv_sec - starttime.tv_sec ) + (endtime.tv_nsec - starttime.tv_nsec)/1000000000;
    }
}

Upvotes: 1

Views: 375

Answers (3)

Filipe Gon&#231;alves
Filipe Gon&#231;alves

Reputation: 21223

The other answers are correct, but your problem seems to be that you're not including the necessary header files.

Add this in your source code:

#include <time.h>

Upvotes: 0

Ritesh
Ritesh

Reputation: 1847

CFLAGS = -g -Wall -std=c99
CC = gcc
LDFLAGS = -lrt

objects = example.o

example: $(objects)
    $(CC) $(CFLAGS) -o example $(objects) $(LDFLAGS)

example.o: example.c
    $(CC) $(CFLAGS) -c example.c
clean:
    rm test $(objects)

As this is linker option, so its best to use as LDFLAGS variable which is common practice in Makefiles.

Upvotes: 0

dbush
dbush

Reputation: 224522

You want to put it on the line that links the executable. Namely, the line that specifies the -o option. That's where the linker phase is carried out.

example: $(objects)
    $(CC) $(CFLAGS) -o example $(objects) -lrt

Upvotes: 3

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