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STL Map Problem

Started by MetaKnight Oct 28, 2004 at 5:48 PM 7 replies 550+ views

Original Post

Oct 28, 2004 at 5:48 PM

Okay im using a map with String key and a pointer to a Texture object, but when i try to acess the Texture object with the string key, it says it doesnt exist, ill just give you relevent parts of the code: this is how i create the map:


std::map<string, lTexture*> TextureList;

this is how i add to the map:


TextureList.insert(pair<string, lTexture*>("mega.dds",new lTexture()));

and this is how i request it(this is where is says it's not there):


TextureList["mega.dds"]->Set();

Fruny

Oct 28, 2004 at 5:54 PM

#include <map>#include <string>using namespace std;struct Foo{  int Set() {};};int main(){   map<string, Foo*> foo;   foo.insert(pair<string, Foo*>("mega.dds", new Foo()));   foo["mega.dds"]->Set();}

Works all right for me (g++ 3.3.4)

What's the exact error message you get?

Qw3r7yU10p!

Oct 28, 2004 at 6:24 PM

When you say it says it doesn't exist, is this at runtime or compile time?

Is it crashing or is it not compiling?

Thygrrr

Oct 29, 2004 at 2:33 AM

Microsoft STL has some bugs AFAIK. This could be one of them? (though I think it was hashed set that was badly crippled)

Qw3r7yU10p!

Oct 29, 2004 at 3:49 AM

Quote:
Microsoft STL has some bugs AFAIK. This could be one of them?

This wouldn't be a bug that had gone unnoticed. Meta is almost certainly doing something wrong in between or isn't posting the real code or has a macro which is messing things up.

We need to know what he means when he says "it's not there". Does he mean it won't compile (which could mean 'Set' isn't a public member of lTexture), or does he mean it crashes?

MetaKnight

Oct 29, 2004 at 6:37 AM

Sorry I wasnt more clear. I meant to say that when I use

TextureList["mega.dds"]

to get a pointer to my texture, it returns a null adress. When the adress should be to my lTexture object.

I found the problem seems to be in here:

When TextureList has a size of 0 and i check to see if there is a lTexture in it, it all of a sudden makes a entry into the map, without an insert command being called. Like this:

Requested *lTexture = NULL;// I check to see if there is a lTexture with the same file in the map// size is 0 here Requested = TextureList[fileName];// now size is 1!! out of nowhere a map entry is made

[Edited by - MetaKnight on October 29, 2004 7:37:24 AM]

Qw3r7yU10p!

Oct 29, 2004 at 7:54 AM

yes, if you read the documentation it says:

Quote:
data_type&
operator[](const key_type& k)
Returns a reference to the object that is associated with a particular key. If the map does not already contain such an object, operator[] inserts the default object data_type().

You need to use find() to check if an entry exists. It returns an iterator pointing to the pair in the map. If it doesn't find anything it will return end().

bkt

Oct 29, 2004 at 8:16 AM

Also suggest that you use STLport, the Microsoft STL is a bit bugged in certian areas.

MetaKnight

Oct 29, 2004 at 8:27 AM

Ah nice

I used a find insted of the [] operator, it works now, thank you all very much.

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