Segfault with String array C++ - c++

Question

Had this program in C and was trying to convert some to C++ as I learn the language. Basically char arrays to strings and some of the input/output. Only issue is I get a segfault when attempting to put the input string into the string array (test2 prints. test3 does not).
Any ideas? Any bad coding habits I should be aware of as I learn c++?
int main() {
int nstr=0, nchar=0, nint=0, nfloat=0;
string input;
int i, z=0;
float inputFloat;
string *strList = (string*)malloc(sizeof(string) * nstr);
char *charList = (char*)malloc(sizeof(char) * nchar);
int *intList = (int*)malloc(sizeof(int) * nint);
float *floatList = (float*)malloc(sizeof(float) * nfloat);
while (z != -42) {
cout << "Input: ";
cin >> input;
cin.ignore();
inputFloat = strtof(input.c_str(), NULL);
if (inputFloat) {
if (fmod(inputFloat, 1.0)) {
nfloat++;
floatList = (float*)realloc(floatList, sizeof(float) * nfloat);
floatList[nfloat-1] = inputFloat;
}
else {
nint++;
intList = (int*)realloc(intList, sizeof(int) * nint);
intList[nint-1] = (int)inputFloat;
}
}
else {
if (input.length() == 1) {
nchar++;
charList = (char*)realloc(charList, sizeof(char) * nchar);
if (input.at(0) == 10)
input = " ";
charList[nchar-1] = input.at(0);
}
else {
nstr++;
cout << "test1" << endl;
strList = (string*)realloc(strList, sizeof(string) * nstr);
cout << "test2" << endl;
strList[nstr-1] = input;
cout << "test3" << endl;
}
}
cout << "Integers: ";
for (i=0; i<nint; i++)
cout << intList[i] << " ";
cout << endl << " Floats: ";
for (i=0; i<nfloat; i++)
cout << floatList[i] << " ";
cout << endl << " Chars: ";
for (i=0; i<nchar; i++)
cout << charList[i] << " ";
cout << endl << " Strings: ";
for (i=0; i<nstr; i++)
cout << strList[i] << " ";
cout << endl << endl;
}
}

Answer 1

As a rule you don't use malloc,calloc,realloc etc. in c++ at all, even though you can.
It less meaningful for simple items like: int, char etc. but when using on objects (like std::string) it cause this kind of problems:
When this line runs:
string *strList = (string*)malloc(sizeof(string) * nstr);
You allocate storage to array of strings, but you didn't called any constructor, therefor all the storage you've allocated is still useless.
In c++ you must use new like this:
string *strList = new string[nstr];
it is shorter, easier and call the constructor of each allocated object.
In the end you dealocate it with delete [] like this:
delete [] strList;
Even better is to use:
vector<string> strList;
and add elements by using:
strList.push_back("something"); or strList.push_back(some_string);
vectors are take care for the memory allocation and free, and are freed automatically as regular object at end of life, so it won't needed to be deleted at all.

Answer 2

realloc reassigns a larger array than the previous one. The new element at the end of the array, you fill it as a integer, float, char , which are basic C types. For C++ objects like strings, the last element in your array is not a new string, one of the possibilities is to create arrays of string pointers.
at the start of your code
string **strList = (string**)malloc(sizeof(string *) * nstr);
and by the end of your code, allocate a new string object at the end of the array.
nstr++;
strList = (string**)realloc(strList, sizeof(string *) * nstr);
strList[nstr-1] = new string(input);
at the end of the program you must delete everything you created through new operator and thru malloc/realloc.
while (nstr--)
{
delete strList[nstr];
}
free(strList);