How to get system environment variables in C language

File Name: get_env.c
Compile instruction: gcc -std = c99 get_env.c -o get_env.out

#include <stdlib.h>
#include <stdio.h>

static inline int readenv_atoi(char *env) {
  char *p;
  // GetENV function is a function of GCC comes with the STDLIB.H header file.
  if (( p = getenv(env) ))
  	return (atoi(p));
  else
	return(0);
}


int main(int argc, char** argv)
{	
	int numprocs = readenv_atoi("OMP_NUM_THREADS");
	printf("numprocs = %d\n",numprocs);
	return 0;
}

Code Source: Source Code of OpenBlas

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