Thread: Help with timersub(), implicit declaration warning!

I am making a program to track how long it takes a user to complete a task.

Everything works relatively fine, but I get a warning on a line and I'm not sure why: "Implicit declaration of function 'timersub' is invalid in C99"

The use of timersub in test(), works, I just don't understand the warning. I thought timersub was covered in time.h.

Here is my code:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#include <time.h>

struct timeval start, stop, res;

void welcome();
void randomize (char *arr[], int n);
void swap (char **a, char **b);
double test (char *arr[], int n);

//Main function
int main()
{
    char *arr[] = {
            "The",
            "quick",
            "brown",
            "fox",
            "jumps",
            "over",
            "the",
            "lazy",
            "dog"
    };

    int n = sizeof(arr)/sizeof(arr[0]); //Get total words in array.
    randomize(arr,n); //Pass array to randomizer.

    welcome();
    double timer = test(arr,n);
    printf("Test took %f seconds to complete.\n", timer);
    return 0;
}

//Function to display the welcome message.
void welcome()
{
    printf("Welcome to the Typing Speed Test.\n");
    printf("You will be given a random permutation of words to type.\n");
    printf("The timer will begin when the first word appears.\n");
    printf("You will not be able to move on to the next word until you\n");
    printf("correctly spell the word provided.\n");
    printf("Press ENTER to begin.\n");
    getchar();
}

//Function to randomize the words in an array.
void randomize(char **arr, int n) {

    gettimeofday(&start,NULL);
    unsigned long time_ms = 1000000 * start.tv_sec + start.tv_usec;
    srand(time_ms);

    for (int i = n-1; i > 0; --i){
        int j = rand()%(i+1);
        swap (&arr[i], &arr[j]);
    }
}

//Function to swap two pointers in an array.
void swap (char **a, char**b)
{
    char *temp=*a;
    *a=*b;
    *b=temp;
}

//Function to run the typing test.
double test(char *arr[], int n)
{

    char str1[20];
    int correct;

    gettimeofday(&start, NULL);
    for (int i = 0; i < n; ++i){
        do{
            printf("Word number %d: %s\n", i+1, arr[i]);
            scanf("%10s", str1);
            if(strcmp(arr[i], str1) != 0){
                printf("Incorrect.\n");
                correct = 0;
            }
            else{
                correct = 1;
            }
        } while (correct == 0);
    }
    gettimeofday(&stop, NULL);

    timersub(&start, &stop, &res);

    return res.tv_sec + res.tv_usec/1000000.0;
}

Any suggestions?

Why not just go without timersub() and return

(stop.tv_sec + stop.tv_usec/1000000.0) - (start.tv_sec + start.tv_usec/1000000.0)

Originally Posted by laserlight

CLion is an IDE, not a compiler. My guess is that you're using the MinGW port of gcc, and if so, this appears relevant: Implicit declaration of timersub() function in Linux - what must I define?

Oh sorry, yes thats correct. I use MinGW via the IDE.

That is, you should configure CLion to provide the compiler with the options -D_DEFAULT_SOURCE -D_BSD_SOURCE

This would be equivalent to writing at the top of each source file:

Code:

#define _DEFAULT_SOURCE
#define _BSD_SOURCE

Normally, #define statements should go after headers, but in this case we want them before the headers (presumably <sys/time.h> in particular) so as to enable certain declarations in the headers. So instead of changing the code in a way that may be meaningless for other compilers on other operating systems, configuring your IDE allows you to make the change for your particular setup.

I will give that a try.

Originally Posted by hamster_nz

Why not just go without timersub() and return

(stop.tv_sec + stop.tv_usec/1000000.0) - (start.tv_sec + start.tv_usec/1000000.0)

My professor is requiring the use of timersub

Originally Posted by confundido

My professor is requiring the use of timersub

Oh, well if that is the case, I would start 'grep'ing (or 'findstr' on windows) through the header files to find which one has it....