Stoi is not a member of std [duplicate]

I'm working on a program where I'm using stoi to convert strings and getting the error in the title. I'm compiling using g++ version 7.3.0 on Ubuntu. The full line I'm entering to compile is g++ -c -std=c++11 -Wall -ansi -pedantic test.cpp Below I included a minimal version of my program that produces the same error.

test.cpp

#include <iostream>
#include <stdio.h>
#include <vector>
#include <fstream>
#include <string>

int main(){
   std::string string = "12"
   int num = std::stoi(string);   //this line causes error
   std::cout << num << std::endl;
}

error

test.cpp: In function `int main()`:
test.cpp:9:20: error: 'stoi' is not a member of 'std'
       int num = std::stoi(string);
                      ^~~~

I'm not sure what could cause this issue, I realize that some of the things i'm including at the top aren't necessary for this program but I just copied them from my actual program into this reproducible example in order to keep everything consistent. Could this be an issue where the compiler Isn't compiling with c++11? I thought the -std=c++11 flag would work but I'm relatively new at this so i could be wrong. Thanks in advance!