Append user input to array in C++ - c++

Question

I'm trying to write a program that asks for user inputs (one at a time, and continues until the user interrupts somehow) and stores them in an array. In python, I can easily append new inputs to the end of an existing list, but this doesn't work in C++. What's the easiest way to do this without involving vectors? I'm thinking of deleting the array each time and creating a new one that's larger, but this seems like a pain.

Answer 1

This is some code I wrote up to do this, it basically creates a new array and copies over data from the old array. Hopefully this can help you. To give you an example of its usage, there is a demonstation area that inputs data from stdin until the user types "END" and the prints it to stdout excluding the "END".
#include <cstdio>
#include <iostream>
#include <cstring>
//Assuming you are storing strings
//Set this to the appropriate max length. The name of this may be misleading,
const int MAX_STRING_LENGTH = 128; //any other suggestions?
char** userInput;
int userInputUsed;
int userInputSize;
void append (char* text, int textLength) {
//If we have used up all the space in the array
if (userInputUsed >= userInputSize) {
//How large you want the new array to be compared to
//the original size (userInputSize)
int newArraySize = 2*userInputSize;
//Create the new array
char** newUserInput = new char*[newArraySize];
//We are only creating the new part of the array
//Another way you could do this is to create the strings as you go
for (int i = userInputUsed;i < newArraySize;i++) {
newUserInput[i] = new char[MAX_STRING_LENGTH];
}
//Copy everything over, I am setting our pointers to the old data
for (int i = 0;i < userInputUsed;i++) {
newUserInput[i] = userInput[i];
}
//Delete the old array
delete[] userInput;
//Set the new array to the old array
userInput = newUserInput;
//Update the size of our array;
userInputSize = newArraySize;
}
//Copy the input to userInput
memcpy(userInput[userInputUsed], text, textLength);
userInputUsed++;
}
int main () {
//Initialise userInput, initialise to whatever size you deem fit
userInputSize = 1;
userInput = new char*[userInputSize];
for (int i = 0;i < userInputSize;i++) {
userInput[i] = new char[MAX_STRING_LENGTH];
}
//Start of demonstration
//Get input until the user types "END"
for (bool running = true;running;) {
char temp[MAX_STRING_LENGTH];
//Scans in until some whitespace, this may not work if
//you want to scan in whole lines which end in '\n'
//scanf("%s", temp);
//or
std::cin >> temp;
//End if input is "END"
if (strcmp(temp, "END") == 0) {
running = false;
} else {
append(temp, strlen(temp));
}
}
//Print out the user input, to see that it is inputed correctly
for (int i = 0;i < userInputUsed;i++) {
//printf("%s\n", userInput[i]);
//or
std::cout << userInput[i] << std::endl;
}
//End of demonstration
//Cleanup our user input
for (int i = 0;i < userInputSize;i++) {
delete[] userInput[i];
}
delete[] userInput;
//Stop the program from ending, you may not need this
//while(true);
return 0;
}
Feel free to comment or suggest improvements to this answer.