Linking external libraries in C++ in Visual Studio Code - c++

Good afternoon! I have a following program in C++, in VS Code. The program reads all data from a table called student. I compile this program with the command g++ retrieveDataFromTable.cpp -I "C:\Program Files\MySQL\MySQL Server 8.0\include" -L "C:\Program Files\MySQL\MySQL Server 8.0\lib" -l mysql -o test, and it perfectly gets compiled. It's my first time that I use an external library in my programs. So, I watched some videos about how linking works, and how to add an external library to our program. Basically, in those videos they used Visual Studio or Codeblocks for adding libraries, but I'm using VS Code. Eventually, I managed to make the program work, but I have some questions. First one is about the way I include header file "mysql.h". I mean it does not look professional. If I were to run this program in other device, of course that would not make any sense. So would anybody like to help me out how I could make it better? My second question is that the program does terminate if I did not have libmysql.dll in my project folder. I'm guessing that it's because I do dynamic linking with the library (please, correct me if I'm wrong). So does anybody know about how I could link this particular library statically? In general, I would really appreciate if anyone would give me some piece of advice about how I could improve this program, and what I should learn to know about these kind of things. Thank you)
#include <iostream>
#include "C:/Program Files/MySQL/MySQL Server 8.0/include/mysql.h"
struct CONNECTION
{
const char *server = "localhost";
const char *user = "root";
const char *password = "password";
const char *database = "project";
};
MYSQL *connection_to_database(CONNECTION connection)
{
MYSQL *newConnection = mysql_init(NULL);
if (!newConnection)
{
std::cout << "Failed to create an object" << std::endl;
std::cout << mysql_error(newConnection) << std::endl;
exit(0);
}
if (!mysql_real_connect(newConnection, connection.server, connection.user,
connection.password, connection.database, 3306, NULL, 0))
{
std::cout << "Failed to connect to database:" << std::endl;
std::cout << mysql_error(newConnection) << std::endl;
exit(0);
}
return newConnection;
}
MYSQL_RES *execute_query(MYSQL *connection, const std::string query)
{
if (mysql_query(connection, query.c_str()))
{
std::cout << "MYSQL query error:\n"
<< mysql_error(connection) << std::endl;
exit(0);
}
return mysql_store_result(connection);
}
int main()
{
CONNECTION id;
MYSQL* connection = connection_to_database(id);
MYSQL_RES* res = execute_query(connection, "SELECT * FROM students");
int rows = mysql_affected_rows(connection);
std::cout << rows << " rows were affected" << std::endl;
int columns = mysql_num_fields(res);
std::cout << columns << " columns in the table" << std::endl;
MYSQL_ROW row;
while((row = mysql_fetch_row(res)))
{
for (int i = 0; i < columns; i++){
std::cout << row[i] << " ";
}
std::cin.get();
}
return 0;
}
I looked some questions but I could not find something useful.

How about using CMake?
You can easily link external libraries into your target executable.
On top of that, is it perfectly supported on vscode by CMake tools extension.
cmake_minimum_required(VERSION 3.25)
project(myProject)
include_directories(${CMAKE_SOURCE_DIR}/include)
link_directories(${CMAKE_SOURCE_DIR}/lib)
add_executable(${PROJECT_NAME} main.cpp)
target_link_libraries(${PROJECT_NAME} libmysql.so)

Thank you guys for your answers! I managed to solve this problem, but I need to do some research why it actually worked (if you could help me I would really appreciate it). Basically I made three directories: build, include, lib. "include" and "lib" directories I copied from MYSQL Server 8.0 directory. The outputs of cmake are stored in "build" directory. I have the following command in CMakeLists.txt:
cmake_minimum_required(VERSION 3.25)
project(myProject)
include_directories(${CMAKE_SOURCE_DIR}/include)
link_directories(${CMAKE_SOURCE_DIR}/lib)
add_executable(${PROJECT_NAME} main.cpp)
target_link_libraries(${PROJECT_NAME} mysql)
And it builds successfully. HOWEVER (!!!) when I try to run it, it just terminates. So I put libmysql.dll in "build" directory and then it ran. I'm really new to these things guys, and this solution of mine probably is not professional. If you guys could recommend me how to improve this procedure, or how to manage to make the program work without libmysql.dll file, I would really appreciate it.

Related

SQLException 32104 in OCCI

I am trying to use OCCI to connect my program to an oracle database but I am getting an SQLException 32104 when I try the createEnvironment function.
My code:
#include <OpenXLSX.hpp>
#include <occi.h>
#include <string>
using namespace OpenXLSX;
using namespace oracle::occi;
int main() {
std::string user = "";
std::string pass = "";
std::string conn_str = "(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.2.159)(PORT=1521))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=test)))";
std::cout << "Initializing Database Connection ......" << std::endl;
try {
Environment* env = Environment::createEnvironment(Environment::DEFAULT);
//Connection *conn = env->createConnection(user, pass ,conn_str);
} catch(SQLException &e) {
std::cout << "Error Message: " << e.getErrorCode() << std::endl;
std::cout << e.getMessage() << std::endl;
}
std::cout << "Initializing Database Connection ......";
std::cout << " OK" << std::endl;
XLDocument doc;
doc.open("Template.xlsx");
auto wks = doc.workbook().worksheet("Extruder Data Log");
int row_number = 4;
char column_letter = 'A';
char column_letter2 = 'A';
std::string loc;
loc = column_letter;
loc += std::to_string(4);
wks.cell(loc).value() = "Hello, OpenXLSX!";
doc.save();
//env->terminateConnection(conn);
//Environment::terminateEnvironment(env);
std::cout << "Program Terminated: Press Enter ...";
std::string wait;
std::cin >> wait;
return 0;
}
I am using CMake to compile:
cmake_minimum_required(VERSION 3.15)
project(Atlas)
set(CMAKE_CXX_STANDARD 17)
# Set the build output location to a common directory
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/output)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/output)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/output)
set(CMAKE_PREFIX_PATH ${CMAKE_CURRENT_SOURCE_DIR}/include/lib)
add_subdirectory(OpenXLSX)
include_directories(${CMAKE_CURRENT_SOURCE_DIR}/include/include/OpenXLSX/headers)
include_directories(${CMAKE_CURRENT_SOURCE_DIR}/include/include/OpenXLSX)
include_directories(${CMAKE_CURRENT_SOURCE_DIR}/include/include/OCCI)
link_directories(${CMAKE_PREFIX_PATH})
find_package(OpenXLSX REQUIRED)
find_library(OCCI NAMES oraocci21.lib oci.lib oramysql.lib oraocci21d.lib ociw32.lib)
add_executable(Atlas Atlas.cpp)
target_link_libraries(Atlas OpenXLSX::OpenXLSX)
target_link_libraries(Atlas ${OCCI})
I have the dlls in the output directory where the executable and libraries end up outputting to.
I figure that it should run, but I am getting a Microsoft C++ exception: oracle::occi::SQLException
and on debugging it shows that it is message 32104 which I know means that it cannot get the error.
The Debug window show that it loads the oraocci21.dll but not any of the other OCCI dlls.
If anyone can let me know what I'm doing wrong I would be incredibly grateful since I have scoured the internet trying to figure this out.
EDIT
Figured out this error, I hadn't moved all of the dlls from the instant client. I was only including the dlls that corresponded to the library names.
I included ocijdbc21.dll, orannzsbb.dll, and oraociicus.dll to the folder with my executable and it now runs past the createEnvironment(Environment::DEFAULT) part.
With this edit, though, I am now running into Error 24960 which says that OCI_ATTR_USERNAME is more than length 255 which it is not.
If anyone can help with that please let me know but I hope that anyone else running across this who needs help sees the part about the dlls.
If it helps to answer my question, I am using instant client base 21_3 and sdk 21_3. I am also using MSVC 16 2019 for compilation with C++17 as the version of C++. My Oracle Database is running on 19c and I can connect to it remotely.
So I figured it out.
I was using this command for cmake:
cmake --build . --target ALL_BUILD --config Debug
This release config command should work because I have debugged the program:
cmake --build . --target ALL_BUILD --config Release
For some reason, I can only assume that OCCI did not like my debugger
version or something like that. If someone could please comment on why this happens I would like to learn.

How to run gdcm examples in ubuntu?

I am trying to run this simple example in GDCM. I have installed the library c++ version and the installation works perfectly fine but I am not able to figure out how to compile and run a example.
#include "gdcmReader.h"
#include "gdcmWriter.h"
#include "gdcmAttribute.h"
#include <iostream>
int main(int argc, char *argv[])
{
if( argc < 3 )
{
std::cerr << argv[0] << " input.dcm output.dcm" << std::endl;
return 1;
}
const char *filename = argv[1];
const char *outfilename = argv[2];
// Instanciate the reader:
gdcm::Reader reader;
reader.SetFileName( filename );
if( !reader.Read() )
{
std::cerr << "Could not read: " << filename << std::endl;
return 1;
}
// If we reach here, we know for sure only 1 thing:
// It is a valid DICOM file (potentially an old ACR-NEMA 1.0/2.0 file)
// (Maybe, it's NOT a Dicom image -could be a DICOMDIR, a RTSTRUCT, etc-)
// The output of gdcm::Reader is a gdcm::File
gdcm::File &file = reader.GetFile();
// the dataset is the the set of element we are interested in:
gdcm::DataSet &ds = file.GetDataSet();
// Contruct a static(*) type for Image Comments :
gdcm::Attribute<0x0020,0x4000> imagecomments;
imagecomments.SetValue( "Hello, World !" );
// Now replace the Image Comments from the dataset with our:
ds.Replace( imagecomments.GetAsDataElement() );
// Write the modified DataSet back to disk
gdcm::Writer writer;
writer.CheckFileMetaInformationOff(); // Do not attempt to reconstruct the file meta to preserve the file
// as close to the original as possible.
writer.SetFileName( outfilename );
writer.SetFile( file );
if( !writer.Write() )
{
std::cerr << "Could not write: " << outfilename << std::endl;
return 1;
}
return 0;
}
/*
* (*) static type, means that extra DICOM information VR & VM are computed at compilation time.
* The compiler is deducing those values from the template arguments of the class.
*/
It has a few header files that it is looking for namely gdcmreader, gdcmwriter and I want to figure out the compiler flags to use to be able to run this file.
I am doing g++ a.cpp -lgdcmCommon -lgdcmDICT but that gives me the error
a.cpp:18:24: fatal error: gdcmReader.h: No such file or directory
compilation terminated.
Can you please help me out? I have searched everywhere but I can't seem to figure out how to run this file.
When using files that are in different locations of your "normal" files you must instruct the compiler and the linker how to find them.
Your code has a #include <someFile.h> command.
The <> usage means "in other path". The compiler already knows common "other paths" as for "stdio" for common libraries.
In case of "not normal", you can tell g++ where to find the headers by adding -Imydir to the command line (replace 'mydir' with the proper path)
For the libraries, static (.a) or dynamic (.so) the same history stands.
The -Lmydir tells g++ where to look for libraries.
Your command line may look like
g++ a.cpp -I/usr/include -L/usr/local/lib -lgdcmCommon -lgdcmDICT
You did not tell how did you install gdcm library, I assume that using apt system. There are two types of libraries, "normal" and "developer" ones. To be able to compile your own software, you need the latter. So, for example in Ubuntu 16.04, type apt-get install libgdcm2-dev. Then all necessary headers will be installed in /usr/include/gdcm-2.6.

Connect To Matlab 2017b from c++ vs2013

I would like to read some variable's value in Matlab from c++. I searched in Internet and found out below example in Matlab Documentation Page.
for using this example I Did below steps:
I add this include path to project :
c:\program files\Matlab\r2017b\extern\include
then I Add this path Library Directory :
c:\program Files\Matlab\r2017b\extern\lib\win64\microsoft
then I Add this library to project :
"libMatlabEngine.lib"
"libMatlabDataArray.lib"
then I placed needed DLLs beside application EXE file.
then I ran the application after that application faced with access violataion error when startMATLAB() Method has been ran.
Note: I had other problem that I resolved it. but I think that problem was very strange and may be knowing that problem help you to find main reason of my problems.
problem was : when I set dll's files path in environment variables my app didn't find dlls and get "no entry point to *.dll" run time error. but when I copy dlls beside of exe, my app saw them.(I restarted VS2013 after change environment variables.)
#include "MatlabDataArray.hpp"
#include "MatlabEngine.hpp"
#include <iostream>
void callgetVars() {
using namespace matlab::engine;
// Start MATLAB engine synchronously
std::unique_ptr<MATLABEngine> matlabPtr = startMATLAB();
// Evaluate MATLAB statement
matlabPtr->eval(convertUTF8StringToUTF16String("[az,el,r] = cart2sph(5,7,3);"));
// Get the result from MATLAB
matlab::data::TypedArray<double> result1 = matlabPtr->
getVariable(convertUTF8StringToUTF16String("az"));
matlab::data::TypedArray<double> result2 = matlabPtr->
getVariable(convertUTF8StringToUTF16String("el"));
matlab::data::TypedArray<double> result3 = matlabPtr->
getVariable(convertUTF8StringToUTF16String("r"));
// Display results
std::cout << "az: " << result1[0] << std::endl;
std::cout << "el: " << result2[0] << std::endl;
std::cout << "r: " << result3[0] << std::endl;
}
I use vs2013 and Matlab 2017b in windows 7.
Thanks for your help.

Have Executable Separated From DLL's (Is That Explicit Linking?)

I want to have my DLL's in a subdirectory of the directory where my executable is. My current directory looks like:
Main Folder: [Folder]
Program.exe
sfml.dll
Assets [Folder]
Picture.png
Music.wav
When I really want it to look like:
Main Folder: [Folder]
Program.exe
Assets [Folder]
Picture.png
Music.wav
MyDlls[Folder]
sfml.dll
When I try to put them (DLL's) in a folder I get the error message:
The program can't start because sfml-system-d-2.dll is missing from your computer. Try reinstalling the program to fix this problem.
So, then I looked into explicit linking, and followed the tutorial here:
http://www.dreamincode.net/forums/topic/118076-dlls-explicit-linking/
If explicit linking is not what I need to use, then please tell me what I need to do. Else, please tell me what is wrong with my code below: (Also, I do not know if this is static or dynamic linking..??)
// Startup.h
#ifndef STARTUP_H
#define STARTUP_H
#include <iostream>
#include <windows.h>
class Startup
{
private:
HINSTANCE hDLL;
public:
// Explicitly link SFML DLL's
typedef int(*funcAdd) (int, int);
typedef int(*funcSubtract) (int, int);
void LoadDLLs()
{
// Retrieve DLL handle.
vector<LPCSTR> libraries = {"openal32.dll",
"sfml-audio-2.dll",
"sfml-audio-d-2.dll",
"sfml-graphics-2.dll",
"sfml-graphics-d-2.dll",
"sfml-system-2.dll",
"sfml-system-d-2.dll",
"sfml-window-2.dll",
"sfml-window-d-2.dll"};
for (int i = 0; i < libraries.size(); i++)
{
hDLL = LoadLibrary(libraries[i]);
if (hDLL == NULL)
{
std::cout << "Failed to load library.\n";
}
else
{
funcAdd Add = (funcAdd)GetProcAddress(hDLL, "Add");
funcSubtract Subtract = (funcSubtract)GetProcAddress(hDLL, "Subtract");
if (Add)
std::cout << "10+10=" << Add(10, 10) << std::endl;
if (Subtract)
std::cout << "50-10=" << Subtract(50, 10) << std::endl;
FreeLibrary(hDLL);
}
std::cin.get();
}
};
#endif
You could register an App Path (see link), making sure you add your Applications alternate DLL folder location to the App Path PATH value.
You cannot do what you want directly. The code you attached will work only for dynamic loading dlls, but it is not the case.
What you want to do will be platform specific and you need to set the path for the library before executing the program.

How to check if a file exists with stat in visual studio c++ 2010?

This is the code I have for checking if a file exists in my visual studio 2010 c++ project:
bool GLSLProgram::fileExists( const string & fileName )
{
struct stat info;
int ret = -1;
ret = stat(fileName.c_str(), &info);
return 0 == ret;
}
I am not sure why it returns false for "shaders/color.vert" when that file really exists, and shaders is a folder in my project main folder.
Can you see something wrong?
THanks
Ok, so to illustrate the quirks of running from the IDE here's a little test I did. Hopefully this should help you figure out how relative paths work in VS.
So my folder hierarchy looks like this:
/_Sandbox
_Sandbox.sln
/Debug
_Sandbox.exe
/shaders
color.vert
/_Sandbox
_Sandbox.proj
main.cpp
The code looks as follows:
#include <iostream>
#include <string>
#include <sys/stat.h>
int main(int argc, char* argv[])
{
struct stat info;
std::string path = "shaders/color.vert"; // To not I get the same behavior with "shaders\\color.vert"
int ret = stat(path.c_str(), &info);
ret == 0 ? std::cout << "File found." << std::endl : std::cout << "File doesn't exist." << std::endl;
std::cin.get();
return 0;
}
So if I run this in the IDE, I get "File doesn't exist.", if I run this outside the IDE, I get "File Found". In order for the program to find the shader file from inside VS I have to put the shader folder like so:
/_Sandbox
_Sandbox.sln
/Debug
_Sandbox.exe
/_Sandbox
/shaders
color.vert
_Sandbox.proj
main.cpp
You can however get the code to find the folder from inside and outside the IDE. What you have to do is go to your project's settings. In "Debugging" and change "Working directory" to $(SolutionDir)$(Configuration)\
Hopefully this clears things up for you.