gprof - output

[Rajesh Munavalli <munavallirv at ornl dot gov>]

Hi,
     I wrote a small program to analyze the execution profile and
understand the usage of gprof. I had "clock()" function to time the
execution along with "gprof" option. Here are the results

gprof output:
-------------
Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
 77.04      6.04     6.04      100    60.40    60.40  testChar()
 22.96      7.84     1.80      100    18.00    18.00  testStr()

clock output:
-------------
testChar     6 seconds
testStr     55 seconds


The results of both are inverse proportional. Could you please explain
the discrepancy in the gprof output?. Or is there something wrong with
the way I am timing the program.

I have attached the program code along with this email for your
reference. 

thanks,

Rajesh
-- 
Rajesh V Munavalli
Computer Science and Mathematics Division
Oak Ridge National Laboratory
P.O.Box 2008 - 1 Bethel Valley Road
Bldg. 5700 - Room R-G216
Oak Ridge TN 37831-6414 USA
Phone: 865-576-6205
Email: munavallirv@ornl.gov

"There are only 10 kinds of people in this world. Those who understand
binary, and those who dont !"

#include<iostream>
#include<time.h>

using namespace std;

time_t ti, tf;
void testChar();
void testStr();

int main()
{
	ti = clock();
	for(int i = 0; i < 100; i++)
	{
		testChar();
	}
	tf = clock();
	cout<<"testChar "<<(tf - ti)<<" "<<(tf - ti)/CLOCKS_PER_SEC<<endl;
	
	ti = clock();
	for(int i = 0; i < 100; i++)
	{
		testStr();
	}
	tf = clock();
	cout<<"testStr "<<(tf - ti)<<" "<<(tf - ti)/CLOCKS_PER_SEC<<endl;
}

void testChar()
{
	char* str_new = (char*) malloc(1000 * 1000 * sizeof(char));
	for(int i = 0; i < 1000; i++)
	{
		for(int j = 0; j < 1000; j++)
			*(str_new + i * 1000 + j) = 'a';
	}
	for(int i = 0; i < 1000; i++)
	{
		for(int j = 0; j < 1000; j++)
			*(str_new + i * 1000 + j) = 'b';
	}
	
	(void) free(str_new);	
}

void testStr()
{
	string str_new = "";
	for(int i = 0; i < 1000; i++)
	{
		for(int j = 0; j < 1000; j++)
			str_new += "a";
	}
	str_new = "";
	for(int i = 0; i < 1000; i++)
	{
		for(int j = 0; j < 1000; j++)
			str_new += "b";
	}
}