How to modify a C program so that gprof can profile it?

Question

When I run gprof on my C program it says no time accumulated for my program and shows 0 time for all function calls. However it does count the function calls.

How do I modify my program so that gprof will be able to count how much time something takes to run?

Answer 1

Did you specify -pg when compiling?

http://sourceware.org/binutils/docs-2.20/gprof/Compiling.html#Compiling

Once it is compiled, you run the program and then run gprof on the binary.

E.g.:

test.c:

#include <stdio.h>

int main ()
{
    int i;
    for (i = 0; i < 10000; i++) {
        printf ("%d\n", i);
    }
    return 0;
}

Compile as cc -pg test.c, then run as a.out, then gprof a.out, gives me

granularity: each sample hit covers 4 byte(s) for 1.47% of 0.03 seconds

  %   cumulative   self              self     total           
 time   seconds   seconds    calls  ms/call  ms/call  name    
 45.6       0.02     0.02    10000     0.00     0.00  __sys_write [10]
 45.6       0.03     0.02        0  100.00%           .mcount (26)
  2.9       0.03     0.00    20000     0.00     0.00  __sfvwrite [6]
  1.5       0.03     0.00    20000     0.00     0.00  memchr [11]
  1.5       0.03     0.00    10000     0.00     0.00  __ultoa [12]
  1.5       0.03     0.00    10000     0.00     0.00  _swrite [9]
  1.5       0.03     0.00    10000     0.00     0.00  vfprintf [2]

What are you getting?