exc_bad_access code 1 error - c++

Question

After a bit of bug searching, I've found that my code leaves with exit code 11 at a certain point, and this is because an EXC_BAD_ACCESS error with code 1. After some googling, I see this must be due to some memory mismanagement, but I'm new to C++ and nothing seems obvious to me.
The code is exiting at the line
fieldFuncts[field](string, equal, validOps, length, difficulty, rng, opGen);
in the file (last function)
//
// Created by Anthony Monterrosa on 4/17/18.
//
#include "MathExpr.h"
#include <list>
#include <iostream>
#include <random>
std::vector<std::function<void(std::vector<MathExpr::CharType> &, MathExpr::NumType &, std::vector<MathExpr::NumType> &)>> MathExpr::layerFuncts;
std::vector<std::function<void(std::vector<MathExpr::CharType> &, MathExpr::NumType &, std::vector<MathExpr::Op> &, unsigned char, unsigned char, std::mt19937 &, std::uniform_int_distribution<MathExpr::OpType> &)>> MathExpr::fieldFuncts;
void MathExpr::init() {
initLayerFuncts();
initFieldFuncts();
}
void MathExpr::initLayerFuncts() {
layerFuncts.resize(Op::EOOE);
layerFuncts[static_cast<unsigned long>(Op::addition)] = [](std::vector<MathExpr::CharType> &string, NumType &equal, std::vector<NumType> & otherArgs) -> void {
string.insert(string.end(), {' ', opToChar(Op::addition), ' '});
equal += otherArgs[0];
std::vector<MathExpr::CharType> digits = intToDigit(otherArgs[0]);
for(int i = 0; i < digits.size(); i++ ) {
string.push_back(digits[i]);
}
};
layerFuncts[static_cast<unsigned long>(Op::subtraction)] = [](std::vector<MathExpr::CharType> &string, MathExpr::NumType &equal, std::vector<NumType> & otherArgs) -> void {
string.insert(string.end(), {' ', opToChar(Op::subtraction), ' '});
equal -= otherArgs[0];
std::vector<MathExpr::CharType> digits = intToDigit(otherArgs[0]);
for(int i = 0; i < digits.size(); i++ ) {
string.push_back(digits[i]);
}
};
}
void MathExpr::initFieldFuncts() {
fieldFuncts.resize(Field::EOFE);
fieldFuncts[static_cast<unsigned long>(Field::integers)] = [](std::vector<MathExpr::CharType> &string, NumType &equal, std::vector<MathExpr::Op> &validOps, unsigned char length, unsigned char difficulty, std::mt19937 &rng, std::uniform_int_distribution<MathExpr::OpType> &opGen) -> void {
std::uniform_int_distribution<MathExpr::NumType> numGen(1, static_cast<MathExpr::NumType>(pow(10, difficulty)));
equal = numGen(rng);
std::vector<MathExpr::CharType> digits = intToDigit(equal);
for(int i = 0; i < digits.size(); i++ ) {
string.push_back(digits[i]);
}
for (int i = 0; i < length - 1; i++) {
MathExpr::Op op = validOps[opGen(rng)];
int count = otherArgsCount(op);
std::vector<MathExpr::NumType> otherArgs(count);
for(int j = 0; j < count; j++) {
otherArgs[j] = (numGen(rng));
}
layer(string, equal, op, otherArgs);
}
};
}
char MathExpr::opToChar(OpType ordinal) {
return opToChar(static_cast<Op>(ordinal));
}
char MathExpr::opToChar(Op op) {
switch(op) {
case Op::addition : return '+';
case Op::subtraction : return '-';
default : return '_';
}
}
MathExpr::NumType MathExpr::otherArgsCount(MathExpr::Op op) {
switch(op) {
case Op::addition : return 1;
case Op::subtraction : return 1;
default : return 0;
}
}
std::vector<MathExpr::CharType> MathExpr::intToDigit(MathExpr::NumType num) {
std::vector<MathExpr::CharType> digits;
while(num >= 10) {
digits.insert(digits.begin(),'0' + static_cast<MathExpr::CharType>(num % 10));
num /= 10;
} digits.insert(digits.begin(), '0' + static_cast<MathExpr::CharType>(num));
return digits;
}
bool MathExpr::initBool = false;
MathExpr::MathExpr(std::vector<CharType> exp, MathExpr::NumType equal) {
if(!initBool) init();
this->string = std::vector<CharType>(exp);
this->equal = equal;
}
void MathExpr::print(MathExpr &exp) {
for(int i = 0; i < exp.string.size(); i++) {
std::cout << exp.string[i];
}
}
void MathExpr::layer(std::vector<MathExpr::CharType> &string, MathExpr::NumType &equal, MathExpr::Op op, std::vector<MathExpr::NumType> &otherArgs) {
layerFuncts[op](string, equal, otherArgs);
}
MathExpr MathExpr::generate(std::vector<MathExpr::Op> &validOps, MathExpr::Field field, unsigned char length, unsigned char difficulty) {
std::vector<MathExpr::CharType> string;
std::random_device rd;
std::mt19937 rng(rd());
std::uniform_int_distribution<MathExpr::OpType> opGen(0, static_cast<MathExpr::OpType>(validOps.size() - 1));
MathExpr::NumType equal;
fieldFuncts[field](string, equal, validOps, length, difficulty, rng, opGen);
return MathExpr::MathExpr(string, equal);
}
here is the corresponding .h file
//
// Created by Anthony Monterrosa on 4/17/18.
//
// EO_E -> "end of _ enum".
#ifndef MATHTESTGENERATOR_MATHEXPR_H
#define MATHTESTGENERATOR_MATHEXPR_H
#include <functional>
#include <random>
#include <vector>
class MathExpr {
public:
using FieldType = unsigned char;
using OpType = unsigned char;
using NumType = short int;
using CharType = char;
enum Field : FieldType {
integers,
EOFE // rational, real, complex.
};
enum Op : OpType {
addition,
subtraction,
EOOE // multiplication, division, absolute value, radical
};
explicit MathExpr(std::vector<CharType>, NumType);
std::vector<CharType> string;
NumType equal;
static void print(MathExpr &);
static MathExpr generate(std::vector<Op> &, Field = Field::integers, unsigned char length = 2, unsigned char difficulty = 1);
//protected:
static void init();
static bool initBool;
static void layer(std::vector<MathExpr::CharType> &, NumType &, Op, std::vector<NumType> &);
static NumType otherArgsCount(Op);
static std::vector<CharType> intToDigit(NumType);
static char opToChar(OpType);
static char opToChar(Op);
static std::vector<std::function<void(std::vector<MathExpr::CharType> &, NumType &, std::vector<NumType> &)>> layerFuncts;
static void initLayerFuncts();
static std::vector<std::function<void(std::vector<MathExpr::CharType> &, NumType &, std::vector<MathExpr::Op> &, unsigned char, unsigned char, std::mt19937 &, std::uniform_int_distribution<MathExpr::OpType> &)>> fieldFuncts;
static void initFieldFuncts();
};
#endif //MATHTESTGENERATOR_MATHEXPR_H
My gut says the error has to do with the "string" vector, but I'm unsure of how to tell. I would appreciate insight into the problem.