Is it possible to use & change global variables in a Static Library? For example:
I declare a
bool test = true;
globally.
Then later in an exported function If the user wants, he can set that test to false. So the program later when checks test if it's true, will notice that it's not true, since one of my function changed it.
Is it right?
I came across the following code today and I was a bit surprised that it worked:-
Code:
std::string func_A () {
static std::string x;
if (!x.empty())
return x;
[Code] ....
I've simplified things slightly - but the basic point is that both functions are in the same source file and they both have a static std::string called 'x'. Being static, I guess they aren't (strictly) local variables. So how does the compiler know that they're different entities? Does it encode their signatures using the function name or something like that? If I call each function separately I do seem to get the correct string...
Here is the code,
Code:
class A {
};
A& CreateObject() {
static A a;
return a;
} static A aa;
int main() {
return 0;
}
So is there any difference between a defined in CreateObject and aa?
I've been reading about libraries; How to make them, how to use them, the different types of libraries, etc..
When using a shared library, does the program require that library to be installed on the computer after the program has been compiled into an .exe?
Ie.. if somebody downloaded a "Helloworld.exe" that I had compiled on my computer using a shared library (that wasn't part of a standard operating system), would they also need that shared library on their computer for the program to run without errors?
and for Static Libraries, when I compile a program using a static library, does it include in the final binary only the functions of the library that are actually used, or does the compiler add in the entire library?
I see many time where static data member is used to count creations of objects -
i.e.
1. the static data member is init to 0
2. the static data member is incremented by 1, in the Class' constructor, every time an object is created
However, if you define a global object of a class,
How can you tell that the static data member is initialized BEFORE the constructor of the global object is called? (i.e. before the global object is created).
Because to my understanding, you do not know in advance the order of global objects' creation -
so the Global Object could be created BEFORE the static data member was created and initialized.
I have made an application and I have basically solved everything. But the only problem is that I am using global variables because it felt like the smoothest, so my program is built on it.
But now I've read around and I understand that you should not use these(?). Do you think pointers is the best think to use instead?I have previously declared my board array and some variables as global and I want them in alot of functions.I have read and understand the procedure for the use of pointers so I can use my int's in the other functions by doing like this? Code: #include <stdio.h>
int justprint();
int main()
{
int Row = 2;
int Column = 2;
int *pRow = &Row;
int *pColumn = &Column;
[code]...
But how do I do it with an array like this one? If I declare it in the main function, and then want to use it in other functions.Or are there better, easier solutions?
Code: char game[3][3]={{0,0}};
On linux, I can compile DLLs (shared objects) as well as executables that use them. I can even access globals and classes that are defined in the EXE from the DLL, and vice versa, simply with the 'export' keyword. flawlessly.
The Problem: But on Windows (using MinGW), no matter what I do, I'm completely unable to access global variables which defined in the EXE, from the DLL. On Linux, this is no sweat, but what's Windows' problem?
I also need to extend classes in the dll with base class method definitions defined in the exe.
Ive heard that on Windows, you need to use declspec(dllimport) and declspec(dllexport). I can compile with CygWin+MinGW/g++4.5.3 as well as "Pure Windows" with MinGW/g++4.7.2 *without* the declspecs. So what's the decljunk for? Is this really just something for MSVC or other compilers?
Here's some Windows code to show what the problem is. The DLL's global variable is accessible to the EXE just fine, but the EXE's global variable is not accessible to the DLL - compilation complains it is an undefined reference.
main.cpp
#include "myLib.h"
#include <stdio.h>
int exe;
[Code].....
edit: I tried using --enable-runtime-pseudo-reloc --allow-shlib-undefined options when compiling the DLL and G++ complains that --allow-shlib-undefined is an unrecognized option.
I am using VS2010 to develop an app which includes several windows forms that I am trying to set up global variables for, and I am getting a few errors like:
LNK2005: "wchar_t *dsn"...already defined in ....obj
I have a header file (externals.h) with:
#ifndef MY_GLOBALS_H
#define MY_GLOBALS_H
extern long dbg;
extern wchar_t dsn[50];
extern wchar_t u[30];
extern wchar_t p[30];
#endif
and 2 different forms, each with different namespaces, but both including the above header (#include "externals.h").One of the form .h files defines the values for these externally declared variables like this: namespace PWValidationTools{
wchar_t dsn[50] =_T("MDOTProjectWise");
wchar_t u[30]=_T("api_admin");
wchar_t p[30]=_T("proce55");
long dbg = 1;
public ref class ValidationSetupForm : public System::Windows::Forms::Form {
}
The other form file only uses these variables, never defines them.I am getting the above LNK2005 error only for the variables declared as wchar_t, not the "long" one. why I'm getting the link errors only for the wchar_t variables.
I am trying to get variables that are global to multiple files. I have mananged to make constant variables that are global but maybe not in the best way. In the header i have the constant variables being defined:
const int variable_Name = 5;
And the cpp file:
#include <iostream>
using namespace std;
#include "vars.h"
int main ( ) {
cout << variable_Name<< endl;
system ("pause");
return 0;
}
Is there a better way to do this and to make the variables able to be changed within the cpp files.
I have a main thread and a worker thread. How do i pass data between them when both are already running without using global variables?
View 1 Replies View RelatedI realize that implicit int rule was removed in C99 but gcc still takes this approach by default. I wonder why this happens:
bbb = 5; // legal
int main(void) {
aaa = 10; // illegal
auto aaa = 10 // legal
Inside function a specifier is needed. Error message with no specifier used is:
error: ‘aaa’ undeclared (first use in this function)
Is this because of linkage - bbb variable has an external linkage so compiler knows that we are defining a variable here while inside mean() we need to show compiler that aaa is defined right here, it does not come from external functions?
I am trying to refresh my memory here as I did some studies many years ago but the results elude me.Also todays c/c++ compilers may have better optimizations.Say I have a static library that includes three obj modules.Each of these object modules has a number of functions. These functions do not reference any other functions within the obj module.My main app links this library but only references one function from each of the object modules.
Question: Are the complete contents of each module linked into my main app or are todays linkers smart enough to just link the functions used?
How to build the static library on my own using visual C++ 2008.
I used the following code to create the header file and cpp of the library.but I am unable to compile due to the following error.
// MathFuncsLib.h
namespace MathFuncs {
class MyMathFuncs {
public:
// Returns a + b
static double Add(double a, double b);
[Code] .....
Error I get while it is compiled :
Error3error C2653: 'MyMathFuncs' : is not a class or namespace name
How to create standalone program. For now I have simple program connecting to MySql Database and when i run it, shows me error, libmysql.dll is missing... When i put libmysql.dll in same folder works. Now my question is, how in code blocks can i compile so i won't require libmysql.dll anymore and be able to use it on any machine.
View 1 Replies View RelatedI have a libcx3d.a which contains my VrmlParser class and other classes which are used by VrmlParser. I have a main.cpp which does this :
VrmlParser vp = new VrmlParser();
double **VOB = vp.getVOB();
When I compile using g++ main.cpp -o main -L. -lcx3d, I get the following errors :
'VrmlParser' was not declared in this scope.
expected ';' before vp.
'vp' was not declared in this scope.
There is a header file called "VrmlParser.h" in the static library. Should I include this header file in main.cpp ? If so, will include "VrmlParser.h" work ? I have the .a and .cpp in the same directory. I can't find the header file for the static library.
I have built a static library that contains a macro. From a separate exe, I am calling this macro, but it doesn't work.
The compilation of the static library and that of the exe went okay.
Static lib contains just the macro definition.
Exe contains call to this macro.
Is there anything else that I need to do for this to work?
I have written a program that uses boost in visual studio 2012. The only boost library I used is filesystem by doing.
1)Properties->Linker->General and adding the path or the .lib to the additional dependencies. The libraries, link at compile time.However when i move the exe to a different computer, it doesn't work. Therefore the libraries were dynamically not statically linked. So my question is how do I statically link the filesystem library, so that i can include boost/filesystem.hpp in visual studio 2012?
There is a file compressor called FreeArc (that has GPL code) and a sub project called Unarc (meant for file extraction only) that is free for any use.
Their source codes can be downloaded from here: [URL] ....
Unarc has a makefile for making a dll. I am trying to make it static instead (.a file), using MinGW, but am failing.
If I use the .o files compiled by the makefile to make one .a file, the decompression methods don't seem to be recognized as they should, so I can't extract anything. These decompression methods are added through static functions called withing the .cpp files of each method, so I guess their code is not being executed.
I am trying to compile a c program for sudoku. I have declare const instances as global variables, but when i try to compile the code it says that my declarations are not constant, here is some of the code.
#include <stdio.h>
#include <assert.h>
const int GRIDSIZE = 3;
const int GRID_SQUARED = GRIDSIZE * GRIDSIZE; //this line
const int ALL_VALUES = (1<<GRID_SQUARED)-1; //and this give//the error
int board [GRID_SQUARED][GRID_SQUARED];
I have a non-MFC static library which I share between a number of different projects, some non-MFC and some MFC. Currently the static library uses a typedef of std::wstring and std::string for UNICODE and non-UNICODE builds.
After discovering it's possible to use CString in non-MFC applications, by including atlstr.h header, I decided I'd rather that than using stl strings and having to keep converting between the different types. However, I seem to be struggling with linker errors when linking the library with a MFC application.
Can I create a non-MFC static library using CString from atlstr.h and link it with a MFC application?
I am trying to build an application that has one static library dependency, however I am getting this error when linking:
1>ClCompile:
1> All outputs are up-to-date.
1>LINK : fatal error LNK1104: cannot open file 'TestWrapperLib.obj'
Why I might be getting that? I have the .lib in the depends line, and the directory where it is at in the include line.
If I have a static variable in a class e.g. a pointer to another class like this: (B is another class)
class A {
public:
static B* cB;
};
Then I set that variable and create multiple instances of class A like this:
A::cB = new B;
As = new A[Number];
Then will the value of cB be the same across all instances?
I cannot pass the class pointer in the constructor as I need to create an array of instances. I tried this method but I get linker error.... unresolved external.
Is it more expensive to use too many static variables instead of ordinary variables? If yes, then how?------------This is a topic given to me to find out about and I don't even know what are static variable except that they live throughout the life of program
and only disadvantage of using static variable instead ordinary variables in my mind is just they will use memory even when we don't need them
For static variables when the memory will be allocated? During compilation or linking or loading time? In below program i am getting error :
(Error C2099: initializer is not a constant in microsoft visual studio) .
If i initialize x = 10 or any constant it works , why?
Code:
main() {
int i=10;
static int x = i;//error ?
if(x==i)
printf("Equal");
[Code] .....
I read in another forum that it is bad practice to declare static variables in a header file? Is that true and if so why.
View 1 Replies View RelatedI've been trying for more than one month to access a method found in a library called libcocosnas_static.a. I'm using Cocos2d-X version 2.0.4. The library has been used many times by my company to make games using cocos2d-1.0.1-x-0.12.0 without any problem.
This is what I've done:
1- I added the include paths of the library to both eclipse and Android.mk
2- Included the .h file using #include "NASPlatformUtil.h"
3- Added the libcocosnas_static.a file to the proj.androidobjlocalarmeabi folder
4- Added "LOCAL_WHOLE_STATIC_LIBRARIES += cocosnas_static" to the Android.mk file
5- Called the function using: NASPlatformUtil:: openUrl("http://xxx.xxx.com/");
I can right click on the function, click Open Declaration and get it without any problem, but the compiler keeps on giving me that dreaded error...