Ошибка terminate called after throwing an instance of 'std::bad_alloc' при работе с типом std::string

void mutation(std::string &mutStr, int &mutRate)
{
 
    int randomNumber = rand();
    int mutOrNot = (randomNumber % 100);
 
    std::string tmpIndivi;
 
    if(mutOrNot < mutRate)
    {
        tmpIndivi = mutStr;
        std::cout << "**********************************" << std::endl;
        std::cout << "Before mutation individ: " << mutStr << std::endl;
        int tmpSize = tmpIndivi.size();
        int randomFlag = (randomNumber % tmpSize);
        randomFlag -= 1;
        tmpIndivi[randomFlag] = randPoint();
        std::cout << "tmpIndivi: " << tmpIndivi << std::endl;
        if(tmpIndivi == mutStr)
        {
            std::cout << "fail mut" << std::endl;
            std::cout << "**********************************" << std::endl;
        } else
        {
            mutStr = tmpIndivi;
            std::cout << "After mutation individ:  " << mutStr << std::endl;
            std::cout << "**********************************" << std::endl;
        }
    }
}

char randPoint() {
 
    char arrPoint[5] = {'A', 'B', 'C', 'D', 'E'};
 
    int randomNumber = rand();
    int rndPoint = (randomNumber % 5);
 
    return arrPoint[rndPoint];
 
}