Not able to access environment variable from C/C++ Program - c++

Question

I am trying to access an environment variable from a C++ program. So I made a test program which works fine :
#include <stdio.h>
#include <stdlib.h>
int main ()
{
printf("MANIFOLD : %s\n", getenv("MANIFOLD_DIRECTORY"));
return(0);
}
Output : MANIFOLD : /home/n1603031f/Desktop/manifold-0.12.1/kitfox_configuration/input.config
Note : Signature of getenv is :
char *getenv(const char *name);
But when I use this as a part of a bigger program with many files linked :
energy_introspector->configure (getenv("MANIFOLD_DIRECTORY"));
Above does not work.
char *a = new char [1000];
a = getenv("MANIFOLD_DIRECTORY");
energy_introspector->configure (a);
Above also does not work.
Note : Signature of configure function :
void configure(const char *ConfigFile);
Error message :
Number of LPs = 1
[Ubuntu10:18455] *** Process received signal ***
[Ubuntu10:18455] Signal: Segmentation fault (11)
[Ubuntu10:18455] Signal code: Address not mapped (1)
[Ubuntu10:18455] Failing at address: (nil)
[Ubuntu10:18455] [ 0] /lib/x86_64-linux-gnu/libpthread.so.0(+0x10330) [0x7f9a38149330]
[Ubuntu10:18455] [ 1] /lib/x86_64-linux-gnu/libc.so.6(strlen+0x2a) [0x7f9a37dfc9da]
[Ubuntu10:18455] [ 2] /home/n1603031f/Desktop/manifold-0.12.1/simulator/smp/QsimLib/smp_llp() [0x5bf8c4]
[Ubuntu10:18455] [ 3] /home/n1603031f/Desktop/manifold-0.12.1/simulator/smp/QsimLib/smp_llp() [0x5a4ac6]
[Ubuntu10:18455] [ 4] /home/n1603031f/Desktop/manifold-0.12.1/simulator/smp/QsimLib/smp_llp() [0x5a4df8]
[Ubuntu10:18455] [ 5] /home/n1603031f/Desktop/manifold-0.12.1/simulator/smp/QsimLib/smp_llp() [0x4283b6]
[Ubuntu10:18455] [ 6] /home/n1603031f/Desktop/manifold-0.12.1/simulator/smp/QsimLib/smp_llp() [0x41e197]
[Ubuntu10:18455] [ 7] /home/n1603031f/Desktop/manifold-0.12.1/simulator/smp/QsimLib/smp_llp() [0x41de7a]
[Ubuntu10:18455] [ 8] /home/n1603031f/Desktop/manifold-0.12.1/simulator/smp/QsimLib/smp_llp() [0x41d906]
[Ubuntu10:18455] [ 9] /home/n1603031f/Desktop/manifold-0.12.1/simulator/smp/QsimLib/smp_llp() [0x41710b]
[Ubuntu10:18455] [10] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5) [0x7f9a37d95f45]
[Ubuntu10:18455] [11] /home/n1603031f/Desktop/manifold-0.12.1/simulator/smp/QsimLib/smp_llp() [0x41697f]
[Ubuntu10:18455] *** End of error message ***
--------------------------------------------------------------------------
mpirun noticed that process rank 0 with PID 18455 on node Ubuntu10 exited on signal 11 (Segmentation fault).
--------------------------------------------------------------------------
But this works :
energy_introspector->configure ("/home/n1603031f/Desktop/manifold-0.12.1/kitfox_configuration/input.config");

Answer 1

getenv returns a pointer to library-allocated memory that is not owned by your program. Your
a = new char [1000]
line shows you did not recognize this and seem to assume you need to supply the memory. That is not true, especially you may never free the memory returned by getenv.
(Even if that would be correct, the simple pointer assignment
a = getenv...
would still be wrong, as you're just swapping a pointer and not copying the memory. That line is a memory leak as you loose the pointer to the allocated 1000 chars)
If you want your program to own that memory so you can later free it, you need to copy it into our private memory space.
a = new char [1000];
e = getenv (<whatever>);
strcpy (a, e);
Unfortunately, I cannot see what you do with the pointer later on in your other examples, especially if you try to free or delete it. Both will lead to an error.

Answer 2

First explicit error in your code is char array allocation and then assigning result of getenv. This leads to memory leak. In your case use:
std::string a = getenv("MANIFOLD_DIRECTORY");
This saves the result in variable a and makes your code immune to unsetting environment variables.
If getenv returns NULL then variable with specified name is not in the environment passed to your application. Try to list all available environment variables with code like below.
extern char** environ;
for (int i = 0; environ[i] != NULL; ++i) {
std::cout << environ[i] << std::endl;
}
If your variable is not listed then most probably it's the problem how you call your application. The other option is that your environment has been unset.