保存命令行参数并进行类型转换

Question

I'm making a c++ program that takes two ASCII characters as input in the command line. It then displays the range between those characters along with the corresponding decimal, octal, and hexadecimal codes for said characters.

The problem I am having is with typecasting the command line parameters.

the command line characters are saved in char* argv[] and if I type cast them directly to an int (for the decimal, octal, hexadecimal) I get some wacky output

if i try saving them in a char variable to then typecast that separate variable into an int it doesn't allow me to save argv[1] into the char. I get this error:

Error: A value of type "char *" cannot be used to initialize an entity of type "char"

Note: the logic for displaying it is not complete. As I am having issues with the command line stuff and wanted to tackle that first

#include <iostream>
#include <iomanip>
using namespace std;

int main(int argc, char *argv[])
{
    //If there are no command line parameters, display this info
    if (argc == 1)
    {
        cout << 

        "This program takes two printable ASCII characters as input, with t"
        "he first\ncharacter preceding the second in the ASCII character se"
        "quence. The program\nthen displays all characters in the range det"
        "ermined by those two characters,\nalong with their corresponding d"
        "ecimal, octal and hexadecimal codes, four per\nline, with a suitab"
        "le header and a pause if the display consumes more than a\nsingle "
        "screen of output. The two input character values must be entered a"
        "s\ntwo separate command-line parameters, and there is no error che"
        "cking.\n\n"

        "The printable ASCII characters extend from the blank space charact"
        "er (' ',\nwith code 32 decimal) to the tilde character ('~', with "
        "code 126 decimal).\nThe characters with codes in the range 0 to 31"
        " and also code 127 are non-\nprintable \"control characters\".\n\n"

        "When entering characters at the command line to determine the char"
        "acter range\nwe want in the output, we need to be very careful how"
        " we enter some characters.\nThese include the the blank space char"
        "acter and some others that are treated\nas \"meta characters\" by "
        "the operating system, and are thus not passed to the\nprogram for "
        "processing.\n\n";

        cout << setw(75) << "Screen 1 of 2" << endl;
        cout << "Press Enter to continue ... ";
        cin.ignore (80, '\n');

        cout << endl;
        cout << "Such characters need to be enclosed in double quotes, except ("
        "of course) for\nthe double-quote character itself (\"), which can be "
        "\"escaped\" by placing a\nbackslash character (\\) in front of it. Her"
        "e is a list of such characters,\nand how they should be entered on the"
        " command line:\n\n"

        "\" \" the blank space\n"
        "\"&\" the ampersand\n"
        "\"<\" the less-than operator, which redirects input\n"
        "\">\" the greater-than operator, which redirects output\n"
        "\"^\" the hat symbol\n"
        "\"|\" the vertical bar, or pipe symbol\n"
        "\\\"  the double-quote symbol\n\n"

        "All other characters can be entered as themselves.\n\n\n\n\n\n\n\n\n";

        cout << setw(75) << "Screen 2 of 2" << endl;
        cout << "Press Enter to continue ... ";
        cin.ignore (80, '\n');
    }
    //Else if there are command line parameters, display decimal, octal and
    //hexadecimal
    else
    {
        char cFirst = argv[1];

        int first = (int)argv[1];
        int last = (int)argv[2];

        int range = last - first;

        if (range == 0)
        {
            cout << "     Dec Oct Hex" << endl;
            cout << setw(4) << argv[1] << setw(4) << dec << first 
                 << setw(4) << oct << first << setw(4) << hex << first << endl;
            cout << "Press Enter to continue ... ";
            cin.ignore (80, '\n');   
        }

        else if (range == 1)
        {
            cout << "     Dec Oct Hex     Dec Oct Hex" << endl;
            cout << setw(4) << argv[1] << setw(4) << dec << first 
                 << setw(4) << oct << first << setw(4) << hex << first;
            cout << setw(4) << argv[2] << setw(4) << dec << last
                 << setw(4) << oct << last << setw(4) << hex << last << endl;
            cout << "Press Enter to continue ... ";
            cin.ignore (80, '\n'); 
        }

        else if (range == 2)
        {
            int middle = first + 1;
            cout << "     Dec Oct Hex     Dec Oct Hex     Dec Oct Hex" << endl;
            cout << setw(4) << argv[1] << setw(4) << dec << first 
                 << setw(4) << oct << first << setw(4) << hex << first;
            cout << setw(4) << (char)middle << setw(4) << dec << middle 
                 << setw(4) << oct << middle << setw(4) << hex << middle;    
            cout << setw(4) << argv[2] << setw(4) << dec << last
                 << setw(4) << oct << last << setw(4) << hex << last << endl;
            cout << "Press Enter to continue ... ";
            cin.ignore (80, '\n'); 

        }

        else if (range >= 3 && range <= 87)
        {
            cout << "     Dec Oct Hex     Dec Oct Hex     Dec Oct Hex     Dec O"
                    "ct Hex" << endl;

            int count = 0;
            for (int i = first; i <= last; i++)
            {
                if (count < 4)
                {
                    cout << setw(4) << (char)i << setw(4) << dec << i << setw(4)
                         << oct << i << setw(4) << hex << i;
                    count++;
                }
                else 
                {
                    cout << endl;
                    count = 0;
                }
            }
        }

        else if (range >= 88)
        {
            cout << "     Dec Oct Hex     Dec Oct Hex     Dec Oct Hex     Dec O"
                    "ct Hex" << endl;
        }


        for (int i=first; i<=last; i++)
        {

            char working = (char)i;
            cout << (char)i << "  " << dec << i << oct << i << hex << i;
        }
        cin.ignore (80, '\n');

    }
}

Answer 1

argv points to array of strings (not characters). To access the first character of arguments you need to do this:

int first = (int)argv[1][0];
int last = (int)argv[2][0];

Also, instead

cin.ignore (80, '\n');   

please use

cin.ignore(numeric_limits<streamsize>::max(), '\n');

Maximum number of characters to extract (and ignore). If this is exactly numeric_limits<streamsize>::max() , there is no limit: As many characters are extracted as needed until delim (or the end-of-file) is found.