Convert from string to int.

Hi folks,
I know this is something that is asked a lot, but I've been reading lots about it and am still none the wiser.

I am reading from file - most values are strings but the odd one is an int. I'm happy reading the int's as strings but I need to convert them into int's so that I can work with them.

At the moment, I have a variable of string type called Length that needs to be an int - thats all!

I've tried many different methods but am failing miserable with all of them!.

I notice a lot use the #include <sstream> however, when I try to include it I get "CdPlayer.h:6: sstream: No such file or directory"
I've also tried the atoil functions without joy.

Thank you!

Code:

---

#include <iostream>
#include <string>
#include <sstream>
using namespace std;

int main ( ) {
    string a = "10";
    istringstream b(a);
    int c;
    b >> c;
    cout << "Result=" << c << endl;
}

---

Works OK with g++
Which compiler are you using?

AFAIK, sstream is the new name, so if you have something really old (compiler wise), you may have some problems.

sprintf()?

Quote:

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Originally Posted by Queatrix

sprintf()?

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Did he not say string to int, not int to string ? :P

I would use the function "atoi".

A stringstream is a bit better than atoi, especially if you're not 100&#37; sure your string is an integer.

If the compiler is too old to use sstream, then perhaps it is time for a new compiler.

If a new compiler is not allowed, then show your attempt using atoi.

My compiler is DevC++ version 4.

I'm afraid I've deleted all my attempts at atoi because they didn't work! Although if I remember correctly, the error that I got when using Atoi was that it couldn't convert a string to a char* bizarrely.. I don't really know why this is.. I'll try and recreate the error for you. Do you have any simple atoi segments that I could try and use to make sure I'm not doing anything stupid?

But yes, include sstream doesn;t work.

Code:

---

#include <iostream>
#include <string>
#include <sstream>
using namespace std;

int main ( ) {
    string a = "10";
    istringstream b(a);
    int c;
    b >> c;
    cout << "Result=" << c << endl;
}

---

Something like that would be ideal for my needs!!

Thanks for your responses.

I've just recreated the atoi error, it is :

Code:

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68 CdPlayer.h  cannot convert `line' from type `string' to type `const char *'

---

the line of code for the conversion is

Code:

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Leigh = atoi(line);

---

Is it because the atoi method requires to be passed a char * and not a string string?!

Quote:

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My compiler is DevC++ version 4.

---

If your IDE is Dev-C++ version 4, it is time to upgrade, either to version 5 (the most recent release of which is 4.9.9.2), or to some other IDE such as Code Blocks. The compiler included by default in Dev-C++ 4 is the MinGW port of GCC 2.95, which is a rather ancient compiler.

My deadline is just a few days away,
I'd rather not have to get used to a new compiler if I don't have too!

Is it something I need to do to get the conversion to work?

Thanks again
L

You could try:

Code:

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Leigh = atoi(line.c_str());

---

Quote:

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Originally Posted by laserlight

You could try:

Code:

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Leigh = atoi(line.c_str());

---

---

Goodness me.

Laserlight - you are wonderful in every way possible!

Thank you very much!

I knew it would be something simple, but just didn't realise how simple! - Thank you again!

(It works fine btw :-p )

THANK YOU!

You are welcome. I do hope you upgrade to a newer compiler for your next C++ project though :)

Quote:

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Originally Posted by laserlight

You are welcome. I do hope you upgrade to a newer compiler for your next C++ project though :)

---

I will I promise :-)

Whilst your here, you couldn't tell me what the keyword is to prevent a variable from dying when a function ends could you?

ie

Code:

---

void function()
{
DONTDIE int a =5;
}

void function2()
{
cout << a;
}

---

There is no such keyword (other than new, new[], and the making of the variable into a global or member variable, but I suspect those are not what you are looking for here).

One option is to return a value from the function, and then call that function from the other function. You might want to read a tutorial on functions, say the one at cprogramming.com

what i want to do is create an integer array.

but i don't know what size it will be until i have ran other functions within the class.

All I want to do is create the integer array inside say function1 and have it available to other functions when function1 has finished...

Basically my app reads a text file and discovers how many cd objects are in the text file, and then creates an int array of that size. Ie 4 cd's = int container[3]

Then a different function re-reads the file to determine how many tracks there are for each cd and then puts them in.
For example, if container[2] contained the value 6 - that would mean there were 6 tracks on cd 3.

But for this to work , I need Container[] to be available to both functions. Can't create it at the beginning because I'll only know how big it should be after function 1 is ran...



Alternatively maybe sort of declare the int array as a global at the top but not set the size of it until midway?
possible? not?

I suggest reaching for a std::vector<int>. You can then also return it from the function, or, if appropriate, it might be more suitable as a member variable instead. The alternative does involve new[], but I would not use it unless I really have to.

Pass an address of a struct (or class) allocated on the heap around then, (as a function arg)

Thank you for your suggestions :-)

I eventually solved it by creating an int pointer.

ie

Code:

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int * temp;

---

then further down just said

Code:

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temp = new int[value];

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Thanks for your help - my assignment (a media player) is almost now complete, got some bugs in it that I'm struggling with but i'll start another thread :-)

Thanks again!
Leigh