difftime not found by linker?

[zgoda]

The standard function difftime from time.h and ctime seems to be not available for linker. The code that uses this function compiles, but I get linker errors:

C+ app/application.cpp
AR out/build/app_app.a
LD out/build/app.out
out/build/app_app.a(application.o):(.text._Z8showTimev+0x10): undefined reference to `difftime'
out/build/app_app.a(application.o): In function `showTime()':
/opt/Sming/Sming/SmingCore/Boards.h:18: undefined reference to `difftime'
collect2: error: ld returned 1 exit status

Sample code that causes this:

#include <SmingCore/SmingCore.h>
#include "user_config.h"

time_t t0;

Timer procTimer;

void showTime()
{
	time_t now = SystemClock.now().toUnixTime();
	Serial.print("elapsed: ");
	Serial.println(difftime(now, t0));
}


void init()
{
	Serial.begin(SERIAL_BAUD_RATE);
	t0 = SystemClock.now().toUnixTime();
	procTimer.initializeMs(2000, showTime).start();
}

Do I need to do anything special to use it?

[mikee47]

Just a note that difftime is available. However, it returns a double float:

double
difftime (time_t tim1,
	time_t tim2)
{
  return (double)(tim1 - tim2);
}

I suspect double is used as historically some platforms used floating-point values to represent time_t. Better to just subtract the two values and stick with integers.