Array limit

[rknight]

#include <iostream>
#include <conio.h>

void input(char *str) {
    bool quit = 0;
    unsigned char key;
    for(int i = 0;quit != 1;) {
        key = getch();
        switch(key) {
            case 8:               // Backspace
            if (i > 0) {
                i--;
                *str--;
                std::cout << "\b \b";
            }
            else
                putch('\a');
            break;
            case 13:             // Enter
            *str = '\0';
            putch('\n');
            quit = 1;
            break;
            default:
            *str = key;
            putch(key);
            i++;
            *str++;
            break;
        }
    }
}

int main() {
    char string[40];
    std::cout << ">";
    input(string);
    std::cout << string;
    getch();
    return 0;
}

I am working on a function that will take input from the user and store it in a string. One problem I face is when the user enters more than the size of the char array. I could set up the input function to take two arguments, the second being the size of the array, but I want to find a more simple way. I want the program to work out how big the array is without me telling it. Does anyone have any suggestions?

[Dani]

I haven't done work with strings in a long while, but could u by any chance use string.h with getline?

Check out this reference site: http://www.msoe.edu/eecs/ce/courseinfo/stl/string.htm

[Valmian]

Use dynamic memory allocation.
In C++ (didn't test):

char * getstring()
{
fflush (stdin); //don't have to do it
char * string=NULL;
char * temp=NULL;
int size =2
scanf(""); //to get buffer input
char ch;
do
{
delete [] string;
string = new char[size];
memcpy (string, temp, sizeof(temp));
delete[]temp;
ch = getc(stdin);
string[size-2] =ch;
temp = new char [size];
memcpy(temp, string, sizeof (string));
size++;
} while (ch!='\n'); //change the quiting value if you want to whatever
return string;
}
void main (void)
{
char * string = getstring();
}

[subtronic]

You're using C++ but you are using the std:string? #include <string>

If you want to do strings C-style which is a pointer to an array of chars like you have you first want to malloc() and then when you want to allocate more space you want to realloc().

[Valmian]

I know, I just had like 1 min so I wrote what came first to my mind.. anyways, I am known to use classes, new/delete and all else in C. (i never took time to learn iostream etc.. but I like objects.. my first though is C)
Ilya

[Bob]

Use dynamic memory allocation.
In C++ (didn't test):

char * getstring()
{
fflush (stdin); //don't have to do it
char * string=NULL;
char * temp=NULL;
int size =2
scanf(""); //to get buffer input
char ch;
do
{
delete [] string;
string = new char;
memcpy (string, temp, sizeof(temp));
delete[]temp;
ch = getc(stdin);
string[size-2] =ch;
temp = new char ;
memcpy(temp, string, sizeof (string));
size++;
} while (ch!='\n'); //change the quiting value if you want to whatever
return string;
}
void main (void)
{
char * string = getstring();
}

Valmian, I really don't wish to be unkind, but it has to be said, the code you posted is horrible. I can't begin to imagine how someone trying to seek advice here would manage with such code, but the problems it introduces would be beyond most of the beginners that come here seeking help, for sure.

No offence, but at the very least I would suggest that if you post code here for people you ought to try compiling it first to check that it'll at least get past your compiler. Failing to do that can leave a poor noob struggling for hours, or days even, trying to overcome the problems in your code.

On top of that, it's clear from your code that you're not sufficiently experienced in C++ to offer advice of the nature you attempted to provide, you're punching above your weight.

All credit to you for coming here and trying to help people, I think that's great. With respect, it might be better if you gained more experience before trying to help further, otherwise you can end up doing more harm than good.

No offence intended.

[subtronic]

I know, I just had like 1 min so I wrote what came first to my mind.. anyways, I am known to use classes, new/delete and all else in C. (i never took time to learn iostream etc.. but I like objects.. my first though is C)
Ilya

In all honesty, I'm using C++ with C too right now because I'm writing a binary file reader to read and load Lightwave objects into a C++ class/object representation (so I can start using my Lightwave models in various applications). In fact, because most all APIs are written in C, like the Python C API and the MySQL C API (not to mention OpenGL), when you're wanting to write a psuedo-OO program (as C++ isn't completely OO) and don't want to bother learning Objective-C which is a pain in the ass, it's probably the only viable way to go (unless you switch programmin languages) -- In my years of working at the Los Alamos National Labs, you'd be so suprised to see how ugly, yet operational most code is. When writing a game engine, its been my experience (not that I have a lot of experience writing game engines), that OO is the best way to go and C++ really lends itself nicely to important OO concepts like inheritance and polymorphism and object message passing (although error handling is less than desirable). For example, there are some things that I need to do with polymorphic STL maps (with dynamic casting) for run-time "type reconstruction".. On the other side though, I hate using cout/cin (because I know for a fact they're just sitting on top of printf which is a far more superior function adding overhead (but you're right, I'm using the STL and C++, why should I be concerned about saving on overhead!!! Hehe)...

So its OK to be a code-bastard as long as you have a clear objective and a purpose for doing so. I think the fact that you're being lazy about your code design will kick you in the ass repeatedly for projects to come. Memory management is something a lot of programmers just don't get and I really think we can attribute a lot of the confusion to deceptively simply commands like new/delete and garbage collectors like the one in Java.

Learn about what each type means in terms of memory usage, where it exists in user space, etc. For instance, writing a loader for binary 3d files requires me to work closely with a spec which involves bitmasking out flags, reading in numbers that could either be either sizeof(char) (which is a constant across all C compilers thank god), sizeof(short), sizeof(int), or sizeof(float)..... I have to take into consideration bit-ordering, since the file is Big-Endian, I have to do byte_swaps and byte_swapping a float is a little tricky ;) because I'm using a x86 processor which is (stupidly) Little-Endian. Good exercise in understanding bytes/bits handling and memory allocation.

[rknight]

Thank you everyone for your help. By the sounds of things, dynamic memory allocation sounds like the best choice. I think one of the main things I wanted to know was if it was possible to find out how much an array can hold by using a pointer; and it looks as if you cant.

Now about the mixture of c and c++ in my code..I must confess that my knowledge in c++ is very small. At the moment I am putting bits of c++ into my c programs to get a taste of what its like.