c++ srand works when I run the program but doesn't work in gdb

Question

c++ srand works when I run the program but doesn't work in gdb. I'm using Ubuntu logged into a terminal. Learning c++. My program runs as it is supposed to if I just execute it. But I really need to start learning to use the debugger. As I step thru the program the call to srand gives the following error.

12      srand(time(NULL));
(gdb) 
__srandom (x=1451559304) at random.c:210
210 random.c: No such file or directory.
(gdb) 
211 in random.c
(gdb) 
210 in random.c
(gdb) Quit

Here is the first part of the program, it is pretty simple.

1 #include <iostream>
2 #include <cstdlib>
3 #include <ctime>
4 #include <string>
5 
6 using namespace std;
7 
8 
9 int main()
10 {       
11         int array_size=0;
12         srand(time(NULL));
13         cout<<"\n\nWhat size of an array would you like?\n";
14         cout<<": ";
15         cin>>array_size;
16         int my_array[array_size];
17         for (int i=0;i<array_size;i++)
18         {
19                 my_array[i]=(rand()%100)+1;
20         }
21         for(int i=0;i<array_size;i++)
22         {
23                 cout<<"\n"<<my_array[i];
24 
25         }

When compiling I use this line.

g++ -g main.cpp -o a

And when I start the debugger it use this.

gdb a

I would appreciate any help. Thanks!

Answer 1

You are stepping into the standard library sources. Assuming you do HAVE the sources, you could set gdb up to find them with dir or set directories . But most people don't have the source for their C standard library - and unless you are actually trying to debug the standard library code itself, I'd suggest using the n (next) command instead of s (step) to step OVER the srand .

Note that the error you are getting is simply that gdb can't find the source file for srand . It will still step through the function eventually - but it will take some stepping, and without source code to view what it's doing, it's pretty pointless.