Get Variable Contents

I was wondering if there was any way, if possible, to retrieve the variable contents? For example:

Code:

---

const char* variable1 = "variable2";
const char* variable2 = "test";

std::cout << variable1;

---

That code outputs "variable2", but I want it to output the contents of "variable2" (I'm using this in a loop where I have an array with different variable names, so thats why I cant just replace variable1 with variable2 in the above example.)

Any help is greatly appreciated. Thanks.

Well, no, C++ does not have a variable variable feature, as does exist in like PHP.

Thanks for the information...I just figured out how to accomplish what I was trying to do without a "variable variable". For those who are asking the same question, this is what I did:

Code:

---

const char* var1 = "test";
const char* var2 = "";
const char* var3[] = {var1, var2};
int a = 2;
int c = 0;

for(int b=0; b<a; b++) {
    if(var3[b]!="") {
          var3[c] = var3[b];
          c++;
    }
}

while(c<a) {
    var3[c] = "";
    c++;
}

---

That's basically all I needed (to remove variables that were blank).

EDIT: This is not a very good example because var3 at the end will equal var3 at the beginning, but this code works for what I was trying to accomplish.

EDIT EDIT: What the above code does is moves the blank entries to the end of the array.

An easier way is to use pointers, which you almost did. Pointers is a kind of variable variable if you would write:

Code:

---

const char* variable2 = "test";
const char* variable1 = variable2;

std::cout << variable1;

---

or:

Code:

---

const char* variable2;
const char* variable1 = variable2;
strcpy(variable2, "test");

std::cout << variable1;

---

it would output the contents of variable2. Notice that you got to declare variable2 before pointing to it, or you won't be able to compile.

In this way it's also possible to write:

Code:

---

int variable1 = 5;
int* variable2 = &variable1; //The & before a variable gets its memory address
std::cout << *variable2; //The * before a pointer gets what's stored at the memory address,  will result in 5
variable1 = 10;
std::cout << *variable2; //Returns 10

---

Maybe you knew this, but from what I understood - this is what you asked about.

Daniel

Thanks for the information. I've never really understood that & and the * and pointers and memory address things (and I know I should attempt to understand them because its a big part of c++).

I think I've accomplished what I wanted to do, but thanks for the information.

Quote:

---

Originally Posted by The Wazaa

An easier way is to use pointers, which you almost did. Pointers is a kind of variable variable if you would write:

...

Code:

---

const char* variable2;
const char* variable1 = variable2;
strcpy(variable2, "test");

std::cout << variable1;

---

it would output the contents of variable2. Notice that you got to declare variable2 before pointing to it, or you won't be able to compile.

...

---

No, variable2 is an uninitialized pointer. You can't just copy data to it (safely) without first allocating space for it to point to.

Oh, I thought that strcpy() did that for you. At least I know that it can extend the allocated space, but when you say it I'm not sure that it allocates new space for you. *Testing* Oh, didn't work. Sorry about that.

EDIT: fixed it :) :

Code:

---

char* variable2 = new char;
char* variable1 = variable2;
strcpy(variable2, "test");

std::cout << variable1;

---

Quote:

---

Originally Posted by The Wazaa

Oh, I thought that strcpy() did that for you. At least I know that it can extend the allocated space, but when you say it I'm not sure that it allocates new space for you. *Testing* Oh, didn't work. Sorry about that.

EDIT: fixed it :) :

Code:

---

char* variable2 = new char;
char* variable1 = variable2;
strcpy(variable2, "test");

std::cout << variable1;

---

---

You expect to copy 5 bytes into a pointer that only points to a buffer of a single byte?

> const char* variable1 = "variable2";
> const char* variable2 = "test";
> std::cout << variable1;

Maybe something like

Code:

---

std::map<std::string, std::string> table;
table["myvariable"] = "test";

---

Then later on, you can do

Code:

---

cout << table["myvariable"];

---

Quote:

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Originally Posted by hk_mp5kpdw

You expect to copy 5 bytes into a pointer that only points to a buffer of a single byte?

---

It works for me, I think I've read somewhere that if the memory allocated in the char* is too small then strcpy makes it bigger. Or maybe I've misinterpreted something about that.

no strcpy will never ever touch the memory.

It works because you were lucky. This program crashes for me for example:

Code:

---

#include <iostream>
using namespace std;


int main()
{
        char foo[] = "abc";        // size = 4 bytes.
        cout << "foo: " << foo << endl;
        strcpy(foo, "abcdefgh");
        cout << "foo: " << foo << endl;
}

---

Hm, strange. I've used things like that forever and never experienced a crash because of that :-/ Well, got to fix that now, and I will not post anything more in this thread since this went a bit off topic. Thanks for the information :) .

If I only knew just a little bit about pointers and memory allocation stuff...

Just wondering, is it bad to have like 6 char[255] variables? Thats like a total of (6 * 255) = 1530 units (whatever these are measured in, I'm assuming bytes).

That's not a lot of space at all, although you would often be better served to have 6 string variables instead.

Well, the way I use these variables, I cant use anything except char[x] where x represents a number.

Really? I honestly doubt that is true. Can you give a reason?

Code:

---


Code:

const char* var1 = "test";
const char* var2 = "";
const char* var3[] = {var1, var2};
int a = 2;
int c = 0;

for(int b=0; b<a; b++) {
    if(var3[b]!="") {
          var3[c] = var3[b];
          c++;
    }
}

while(c<a) {
    var3[c] = "";
    c++;
}

---

wouldn't code like that give you a compiler error because var3 is const

^^ That code works for me and I use const...

Well, after thinking about my source code and looking at it, there are only two functions that I use that require my variables to char. The first one is the mysql_query function. I know I can use some conversion from string to char (since I already have a little bit of a string to char in my code). The other one is GetWindowText function. I dont know if the variable that it stores to can be a string or not, but I dont know if I never try.

Well, I got two conversion functions, one from char to string and one from string to char...I only need these functions because the only way to GetWindowText is to use a char variable. Then I convert the char variable to a string variable and vice versa for SetWindowText. string variables make it much easier!!! I never knew string variables were as easy to use as they are (reminds me slightly of PHP variables, but not quite).

When I tried finding string to char and char to string functions, people were saying (on other sites) that its impossible or nearly impossible. If anyone is doing the same thing, here are my functions (very short functions cuz I like short functions):

Code:

---

string convert2string(const char* char_var) {
    string string_var;
    string_var.insert(0,char_var);
    return string_var;
}

char* convert2char(string string_var) {
    int a = 0;
    int b = string_var.size();
    char* char_var = new char[b+1];
    while(a<b) {
          char_var[a] = string_var.at(a);
          a++;
    }
    char_var[b] = '\0';
    return char_var;
}

---

If anyone has any shorter functions, then please post.

Code:

---

string convert2string(const char* char_var) {
    return char_var;
}

const char* convert2char(string string_var) {
    return string_var.c_str();
}

---

You don't actually need these functions. For GetWindowText, use a local character array to get the text and then assign that to the string. SetWindowText takes a const char* (not a plain char*), so you can just pass it the results of c_str().

Thanks for the info on the c_str(). I didnt know that. Before, when I tried setting the string variable to a char[x] (where x is a number), it gave me a compiler error. Now that I tried it again, it actualy worked ( GetWindowText(TEXTFIELD,somevarthatsachar[x],x); string = somevarthatsachar[x]; ). I still need convert2char because I have a query string variable and mysql_query only takes const char* and I have a SendMessage where I update the status bar with a string and it has to be (LPARAM)char (I'm not quite sure exactly which type of char or const char or whatever).

EDIT: I forgot to apply the info I learned for the c_str() to the mysql_query function, so I can use string_var.c_str() instead of converting it. Only need to find a way for the SendMessage without the functions.

EDIT EDIT: Just tested string_var.c_str() in the SendMessage function and it worked.

EDIT EDIT EDIT: Is there any way to store the GetWindowText into a variable without defining the size of the variable?

THANKS for your help!!!!!!!!!!!!!!!!!! :) :) :) :)

Does getWindowText() return a char*? Then you can do

std::string str = getWindowText();

straight away. This operation is defined for std::string and works as expected.

>> Is there any way to store the GetWindowText into a variable without defining the size of the variable?
No, unless you use the MFC CString version of GetWindowText. If you'll notice, the version that takes a char* also takes a maxCount number of characters, because with C style strings you have to define the size of the array before you pass it to the function, and the function doesn't want to overrun the array bounds. So what you have to do is define the array to be the maximum number of characters you think will be returned from GetWindowText.

>> Does getWindowText() return a char*?
Nope, it takes a pointer as an output parameter.

getWindowText( DlgEdittextInt, char*, int )

I believe thats the "arguments" (using a PHP word, not sure if it applies to C++). char* is the variable to store the entered text to. int is the max number of characters to retrieve from the entered text (so really, my previous question becomes stupid because I would have to define this value and I might as well define a "char array" with the int value number of values. Me being the stupid me, I just realized I would only need one char array variable, for example:

Code:

---

char var[255];
string var1, var2, var3;
....
GetWindowText( THETEXTFIELD1INT, var, 255);
var1 = var;
GetWindowText( THETEXTFIELD2INT, var, 255);
var2 = var;
....

---

Before, I had a different "char array" for each edittext box.

Did I mention, by switching to use strings, I was able to decrease the size of my .exe by four times (it was 2mb and now its .5mb). I was using a regex header before to return some things within the variables, but now with string.find() and string.substr() and string.erase(), I'm able to do all the regex things I was doing before. However, its still uses approx. 4000 [units] of memory, which isnt that bad compared to some other programs.