Three questions regarding command line arguments / char* - c++

Question

My post is organized in three sections:
1. My code
2. Example input and output
3. My three questions
MY CODE:
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <iomanip>
#include <fstream>
#include <sstream>
#include <string>
#include <cstring>
using namespace std;
void deleteTrash(char*, char*);
const int kStr = 2;
const int kStrLen = 3;
int main(int argc, char* argv[])
{
if (argc < 4) {
cout << "Incorrect argument given." << endl;
cout << "Try again." << endl;
return 0;
}
cout << "PRINT argv[2]" << endl;
cout << "-----" << endl;
for (int i = 0; i < sizeof(argv[2]); i++) {
cout << "Iterator: " << i << endl;
cout << argv[2][i] << endl;
}
char* inputString;
deleteTrash(argv[kStr], inputString);
cout << "PRINT inputString" << endl;
cout << "-----" << endl;
for (int i = 0; i < sizeof(inputString); i++) {
cout << i << endl;
cout << inputString[i] << endl;
}
int strLen;
stringstream num;
num << argv[kStrLen];
num >> strLen;
if ( num.fail() ) {
cout << "Incorrect argument given." << endl;
cout << "Try again." << endl;
return 0;
}
if ( strLen < sizeof(inputString) ) {
cout << "Incorrect argument given." << endl;
cout << "Try again." << endl;
return 0;
}
return 0;
}
void deleteTrash(char* tempString, char* inputString)
{
int tempStringLen = sizeof(tempString);
int newSize = 0;
while (tempString[newSize] != '\0')
newSize++;
char newString[newSize + 1];
int iterator = 0;
while (tempString[iterator] != '\0') {
newString[iterator] = tempString[iterator];
iterator++;
}
newString[newSize] = '\0';
cout << "PRINT newString" << endl;
cout << "-----" << endl;
for (int i = 0; i < sizeof(newString); i++) {
cout << newString[i] << endl;
}
inputString = newString;
cout << "PRINT inputString" << endl;
cout << "-----" << endl;
for (int i = 0; i < sizeof(inputString); i++) {
cout << "Iterator: " << i << endl;
cout << inputString[i] << endl;
}
return;
}
EXAMPLE INPUT:
./hw1q5 4 W# 3
OUTPUT:
PRINT argv[2]
-----
Iterator: 0
W
Iterator: 1
#
Iterator: 2
Iterator: 3
3
Iterator: 4
Iterator: 5
T
Iterator: 6
E
Iterator: 7
R
PRINT newString
-----
W
#
PRINT inputString
-----
Iterator: 0
W
Iterator: 1
#
Iterator: 2
Iterator: 3
Iterator: 4
Iterator: 5
Iterator: 6
Iterator: 7
PRINT inputString
-----
0
Segmentation fault: 11
MY QUESTIONS:
Why does argv contain more than 3 elements (M, #, and \0). It prints out 8 elements (print statement iterates 0 - 7), which, after W, #, \0, are garbage. Should it not be printing only the 3 elements (M, #, and \0). Why is this happening? How may I fix it?
Why is it that when I set newString (type char) to inputString (type char*), by doing inputString = newString, inputString iterates 8 time in the print statement, printing blanks after printing M, #, and \0.
Why is the seg fault happening in the third statement?

Answer 1

sizeof() does not return the length of a null-terminated character array string. Instead you need something like strlen().

Answer 2

Let's just take one of the problems here:
// Wrong!
int main(int argc, char* argv[])
...
for (int i = 0; i < sizeof(argv[2]); i++) {
cout << "Iterator: " << i << endl;
cout << argv[2][i] << endl;
}
// Better
int main(int argc, char* argv[])
...
for (int i = 0; i < argc; i++) {
cout << "argv[" << i << "]: " << argv[i] << endl;
}
argv[] is an array of one or more "C" strings.
argc tells you how many strings are in the array.
You want to iterate through the strings in the array (argv[i]), not the characters in the string (for example, "argv[0][0]").
... AND ...
"sizeof(argv)" just gives you the size of a pointer (4 bytes, for a 32-bit CPU). It does NOT give you the #/elements in the array. That's what "argc" is for.

Answer 3

In answer to your first question, I'm going to refer you to another SO article: What does int argc, char *argv[] mean?
The first command line argument is always the command itself. So in your example:
./hw1q5 4 W# 3
There are four command line arguments: hw1q5, 4, W#, and 3.
In regards to your other questions, and the remainder of the first question, the majority of your problems stem from the assumption that sizeof(char*) returns the length of a null terminated string, which it does not (as has been pointed out both in comments and an earlier answer).
A good reference for understanding sizeof can be found here: http://en.cppreference.com/w/cpp/language/sizeof, or as I suspect this is a homework assignment based on your compiled program name, your C++ textbook.