This is my first time asking a question on stack overflow so please bear with me
I am trying to create a calculator in c as a project but I am getting a segmentation fault when evaluating a algebraic expression for second time using a python lib inside c using Python.h
At first I was using the eval function directly provided by the python interpreter but after reading about why eval can be dangerous I used a python lib named NumExpr as suggested here but when I use that python library to evaluate the algebraic expression I get a segmentation fault on entering the expression second time (it works for the first time)
Here is the example code :
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <Python.h>
void my_pause()
{
int c;
printf("\n Press the enter key to continue...");
fflush(stdout);
while ((c = getchar()) != '\n' && c != EOF) {}
}
void main()
{
char selec[8], temp;
while(1)
{
main:
printf("Enter here : ");
scanf("%s" , selec);
scanf("%c" , &temp); //this scanf is necessary as it solves the input buffer
if(strcmp(selec,"math-exp")==0)
{
printf("\n\n Please note the opreators : ");
printf("\n for addition '+'");
printf("\n for subtraction '-'");
printf("\n for multiplication '*'");
printf("\n for division '/'");
printf("\n for exponential power '**'");
printf("\n for percentage '%%'");
printf("\n for knowing about various functions that can be used please check documentation");
//I had to print this using printf and not by python print itself is to solve the EOL error
printf("\n\n Enter the mathematical expression : ");
Py_Initialize();
PyRun_SimpleString("import numexpr as ne");
PyRun_SimpleString("math_exp = input()");
//I had to print this using printf and not by python print itself is to solve the EOL error
printf("\n The answer is : ");
fflush(stdout);
PyRun_SimpleString("print(math_exp)");
Py_Finalize();
my_pause();
system("clear");
goto main;
}
else if(strcmp(selec,"exit")==0)
{
exit(0);
}
}
}
This works perfectly fine for the first time but if you enter 'math-exp' for the second time to enter another expression it will show the segmentation fault. I am using linux mint, gcc 9.4.0, python 3.8. Below is the command I am using to compile the code :
gcc test.c -o test.bin -I"/usr/include/python3.8" -L"/usr/lib/python3.8" -lpython3.8
Thanks in advance for the help!
Calling Py_Finalize
multiple times creates memory leaks. Just move your Py_Finalize
line before exit(0)
This bug has been opened in 2007, and just closed last month. https://bugs.python.org/issue1635741
Solved in python 3.11.