Thread: Syntax Issue - Namespace and Proper Way to Declare

I'm working step by step with simple things to make sure I'm getting C++ syntax correct (especially with namespaces, and pointers!).

I'm working with Poppler, a library for working with PDF files. There is, apparently, no constructor for a Poppler Document. Once I have the document object, I can load_from_file(), though.

The problem I'm having is that I am trying to declare the object pDoc, then use it in a loop. In each iteration, I'm going to load a new file into pDoc.

Here is the link to the docs that cover the poppler::document class:

https://oinksoft.com/doc/poppler/cpp...1document.html

I do notice that the load_from_file() is static, so my assumption is that I use it to create a document (since there's no constructor), but I'm not clear on the syntax and formatting.

Right now I have:

Code:

...
#include "poppler/cpp/poppler-document.h"
using namespace std;
...
void addPDFs(list<string> fList) {
   list<string>::iterator iList;
   poppler::document pDoc;      //Problem Line #1
   int x = 1;
   int pNum = -1;


   for (iList = fList.begin(); iList != fList.end(); iList++) {
      pDoc.load_from_file(*iList);
      pNum = pDoc.pages();      //Problem Line #2
      cout << "Item : " << x << " : " << *iList << ", Total Pages: "
            << pNum << endl;
   }
}

(There may be other errors in my code - I can look them up and find them through debugging and I'll remember them better that way, but I'm having trouble with this one because I can't find any example code for this class.)

I'm having problems with two lines (marked with comments). In the first I'm declaring pDoc (and eventually it will be used outside of the loop). When I compiled this program, Eclipse gave me the error, "no matching function for call to 'poppler::document::document()'" (The point that it seems to know what's available makes me think I'm at least referring to the poppler::document object correctly.)

What I don't see is how to declare pDoc here properly (I don't want to load a file in yet).

Then, on the 2nd problem line, I think that should be something like:

Code:

pDoc = poppler::document::load_from_file(filename)

I'm willing to bet that the answer is pretty obvious - I'm just not sure how those two lines should be written to declare pDoc and, later, to load in the file and create a new instance.

Code:

poppler::document *pDocument = poppler::document::load_from_file(...);

Originally Posted by TangoOversway

Okay, I see - and it makes sense. I missed the obvious. Thank you, brewbuck.

So this is something I can't really declare until I create it with that statement?

No, you could just initialize the pointer to NULL until you're ready to open the document. But if you try, you can usually find a way to not actually declare that variable until right before it gets used the first time. There are times when that's not possible, but I doubt this is one of those times.

Also, I don't know the Poppler API in detail, but you probably need to call delete on that pointer when you are done with the document and ready to open the next one -- otherwise you'll leak memory like crazy.

You should let them know, if possible, that it's better to throw an exception on failure than returning a pointer, and if returning a raw pointer is a must, then it should absolutely be declared in the documentation if it should be deleted or not.
I can't really seem to find any reference to the poppler library from the main page...

Originally Posted by Elysia

You should let them know, if possible, that it's better to throw an exception on failure than returning a pointer, and if returning a raw pointer is a must, then it should absolutely be declared in the documentation if it should be deleted or not.
I can't really seem to find any reference to the poppler library from the main page...

There are significant issues throwing exceptions across DLL boundaries. Every component involved must be linked against the same C++ runtime. That is often impossible to assure when using collections of third party code. I wish it wasn't so... But it is.

Poppler is derived from xpdf, which itself was written in a very C-like way. I made some relatively minor contributions to that code base in a past life (having to do with how it identifies, handles, and reports errors). xpdf, and I assume Poppler, are good solid code, but not the best example I've seen of perfect API design. It could be much worse, though.