It's hard to determine exactly what's happening because your post
doesn't explain where you're using this variable, but note that extern
variables cannot be used across module boundaries. For example,
nsBrowserApp.cpp get compiled into firefox.exe, whereas most of our code
gets compiled in xul.dll. If you define an extern variable somewhere in
firefox.exe, you cannot use it from xul.dll. If you need this kind of
cross module access, you need to export a function/variable from one
module and import and call it in the other, using MOZ_EXPORT and
MOZ_IMPORT_API and friends.
On 2014-10-24 8:36 AM, Josip Maras wrote:
Hi,
I'm extending the Firefox source in order to log some information during web
app execution, for example event, script executions, new element creations,
removals, attribute modifications, etc. Since these things occur often, when I
load a more demanding application (e.g. facebook), everything hangs for a
while, because there is a large number of relatively small pieces of
information being written to a file.
Because of this, i was thinking of doing it in batches, having one global
extern stream variable where all longs are added to, and when enough
information gets accumulated to write it to a file, and avoid these hangings.
Since I'm a noob C++ "programmer" I will paste some code of what i've done,
just in case:
I have one header file with the extern variable:
-- FC_ExternStreamDeclaration.h --
#ifndef FC_EXTERN_VAR_DECL_H
#define FC_EXTERN_VAR_DECL_H
#include <stdio.h>
#include <sstream>
#include <fstream>
extern std::stringstream FC_LOG_STREAM;
#endif //FC_EXTERN_VAR_DECL_H
and one header with the logging functionality
-- FC_Log.h --
#pragma once
#ifndef FC_LOG_H
#define FC_LOG_H
#include <stdio.h>
#include <sstream>
#include <fstream>
#include "FC_ExternStreamDeclaration.h"
inline void WriteToStream(const char** fragments, int length)
{
//add to stream
//if stream big enough write to file
}
#endif //FC_LOG_H
and in nsBrowserApp.cpp where the main function is defined, i define the
variable and include the headers
----- nsBrowserApp.cpp ---
#include "FC_ExternStreamDeclaration.h"
#include "FC_Log.h"
std::stringstream FC_LOG_STREAM;
And then, in each file from which i do logging, i include the header files and
call the WriteToStream function. For example, I'm doing it from
Interpreter.cpp, Eval.cpp, nsINode.h, etc. (all over the code).
And i thought that this will be enough. However, i get: error LNK2001
unresolved external symbol stringstream FC_LOG_STREAM. If i define it there,
the compilation succeeds, but I effectively get two different streams, one for
the JavaScript execution, and the other for the DOM and the rest of the browser.
I'm thinking this happens because these variables are in different dlls.
I would be grateful for any tips about fixing it.
Sorry for the long question.
Thank you,
Josip
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