I'm stumped... it took me a while to track this down.. because I don't have visual C++ IDE installed on the problematic system (it is windows server 2019)... my code works fine with VS 2022 on my laptop (W11 22H2)... anyhow.. I get this exception
Cannot create a file when that file already exists
I tracked it down to this code:
const auto fileTime = fs::last_write_time(p);
apparently this function can also write to the file to modify the time.
but I'm just trying to read it... (I didn't add the arguments necessary to write)
does anyone have any idea why this error might be happening?
https://en.cppreference.com/w/cpp/filesystem/last_write_time
please note it is highly likely that sometimes the file is actually being written to when I call this code (this code is called in a loop, and so is the file that is being written by another program)
The Point Cloud library comes with an executable pcl_hdl_viewer_simple that I can run (./pcl_hdl_viewer_simple) without any extra arguments to get live data from a Velodyne LIDAR HDL32.
The source code for this program is supposed to be hdl_viewer_simple.cpp. A simplified version of the code is given on this page which cannot be compiled readily and requires a tiny bit of tweaking to make it compile.
My problem is that the executable that I build myself for both the versions are not able to run. I always get the smart pointer error "Assertion px!=0" error. I am not sure if I am not executing the program in the correct way or what. The executable is supposed to be executed like
./hdl_viewer_simple -calibrationFile hdl32calib.xml -pcapFile file.pcap
in case of playing from previously recorded PCAP files or just ./hdl_viewer_simple if wanting to get live data from the real sensor. However, I always get the assertion failed error.
Has anyone been able to run the executables? I do not want to use the ROS drivers
"Assertion px!=0" is occurring because your pointer is not initialized.
Now that being said, you could initialize it inside your routines, in case the pointer is NULL, especially for data input.
in here, you can try updating the line 83 like this :
CloudConstPtr cloud(new Cloud); //initializing your pointer
and hopefully, it will work.
Cheers,
So I`m writing an application for an embeded system (Linux on ARM) and everything works fine, until I decide to add one more class at the start of a main function. It looks like this (can not post the actual code here):
int main ()
{
Someclass class1;
....
}
And after that application just return code 1 (generic error) right from the start. If I remove it - everything is fine again. To me it looks like I ran out of stack space - but in that case system should throw a SIGSEV or SIGSTKFLT. But there was nothing just error code 1. I tried to get stderr like that:
./app 2> error.log
But there was also nothing.
Tried to debug using remote gdb:
Client:
Cannot access memory at address 0x3030204
Cannot access memory at address 0x3030200
Server:
Remote debugging from host xxxxxx
readchar: Got EOF
Remote side has terminated connection.
Details:
I`m wirting on C++11 (TR1) (project-specific), compile with GCC 4.4.6 (also project-specific), debug with GDB 7.4
Solved
Big thanks to everyone who responded, I have managed to solve this, and it was my fault - I did not initialized device`s libraries correctly before calling a wrapper class (later they were initialized and thus it worked). Thank you all again.
The most obvious place to look would be in the class' constructor which is being called on invocation of main.
I am writing a program for Windows that eventually has to launch a different pre-existing .exe that sits on the same computer. It passes multiple parameters to this .exe file. I am reading the actual command and parameters and constructing the command but I also tried hard coding it with the same results. Here's the hard coded version (I picked this out of an older C program that uses the same.exe):
system("c://IQapture//dmon2_6_IHD -p2 c://IQapture//mon_table_101_Tx8.txt 11 0 0");
So in the original program inside int _cdecl main(int argc, char**argv) this use of system works. In my C++ program inside a C++ class method when I issue the command the correct program launches but it immediately puts up an error dialog stating that an error has occurred. I echo'd the system string used to launch the exe out to the console. Right after it fails, I copy and paste the same line that was echo'd and this time the exe runs without error. This is repeatable. In case it was timing related I tried adding a 10 second delay before issuing the system command but it didn't matter. Plus the original older program doesn't require a delay. This implies to me that the string is correct and the target program works. Somehow the system() invocation is different from a direct command line invocation. The program compiles and builds fine. I'm using Visual Studio 2010.
Does anyone have ideas on how to make the system() invocation work like the command line invocation?
That really doesn't look like the kind of thing that Windows would be happy with... Try it with backslashes instead:
system("c:\\IQapture\\dmon2_6_IHD -p2 c:\\IQapture\\mon_table_101_Tx8.txt 11 0 0");
If that still doesn't work, you quite likely have one of the following issues:
Your current working directory is wrong;
An environment variable is missing;
Your program is running with the wrong user permissions;
Your program is tying up a resource that the spawned process requires (eg you have not closed a file that it requires as input).
There are a lot of things to consider - the environment, the user running the program, the parent process and what's inherited... Take a look at the parameters to the CreateProcess function. Chances are your system call's invocation isn't matching the command line's (though that may not be the issue, simpler things are more likely.)
I'd advise working backwards from the error to rule out simple causes such as the environment, current directory, etc. before delving into such things as creation flags and security attributes.
You have your slashes backwards. Try:
system("c:/IQapture/dmon2_6_IHD -p2 c:/IQapture/mon_table_101_Tx8.txt 11 0 0");
You can use the backslash \ but because that is an escape sequence starter in a string (for C/C++) that is why you use two in a row. As the compiler will convert \\ into a single slahs in the string:
Thus:
system("c:\\IQapture\\dmon2_6_IHD -p2 c:\\IQapture\\mon_table_101_Tx8.txt 11 0 0");
// Is equivelent to the command line string:
> c:\IQapture\dmon2_6_IHD -p2 c:\IQapture\mon_table_101_Tx8.txt 11 0 0
But Windows has supported both types of slashes for longer than I can remember. So the following command line is equivalent.
> c:/IQapture/dmon2_6_IHD -p2 c:/IQapture/mon_table_101_Tx8.txt 11 0 0
Using '/' in a string (in C/C++) does not require escaping. So you just need to use it as is:
system("c:/IQapture/dmon2_6_IHD -p2 c:/IQapture/mon_table_101_Tx8.txt 11 0 0");
I'm getting really strange behavior in one of the DLLs of my C++ app. It works and loads fine until I include a single file using #include in the main file of the DLL. I then get this error message:
Loading components from D:/Targets/bin/MatrixWorkset.dll
Could not load "D:/Targets/bin/MatrixWorkset.dll": Cannot load library MatrixWorkset: Invalid access to memory location.
Now I've searched and searched through the code and google and I can't figure out what is going on. Up till now everything was in a single DLL and I've decided to split it into two smaller ones. The file that causes the problems is part of the other second library (which loads fine).
Any ideas would really be appreciated.
Thanks,
Jaco
The likely cause is a global with class type. The constructor is run from DllMain(), and DllMain() in turn runs before LoadLibrary() returns. There are quite a few restrictions on what you can do until DllMain() has returned.
Is it possible that header includes a #pragma comment(lib,"somelibrary.lib") statement somewhere? If so it's automatically trying to import a library.
To troubleshoot this I'd start by looking at the binary with depends (http://www.dependencywalker.com/), to see if there are any DLL dependencies you don't expect. If you do find something and you are in Visual Studio, you should turn on "Show Progress" AKA /VERBOSE on the linker.
Since you are getting the Invalid Access to memory location, it's possible there's something in the DLLMAIN or some static initializer that is crashing. Can you simplify the MatrixWorkset.dll (assuming you wrote it)?
The error you describe sounds like a run-time error. Is this error displayed automatically by windows or is it one that your program emits?
I say attach a debugger to your application and trace where this error is coming from. Is Windows failing to load a dependency? Is your library somehow failing on load-up?
If you want to rule in/out this header file you're including, try pre-compiling your main source file both with and without this #include and diff the two results.
I'm still not getting it going. Let me answer some of the questions asked:
1) Windows is not failing to load a dependency, I think since Dependency Walker shows everything is ok.
2) I've attached a debugger which basically prints the following when it tries to load MatrixWorkset.dll:
10:04:19.234
stdout:&"warning: Loading components from D:/ScinericSoftware/VisualWorkspace/trunk/Targets/bin/MatrixWorkset.dll\n"
10:04:19.234
stdout:&"\n"
status:Stopped: "signal-received"
status:Stopped.
10:04:19.890
stdout:30*stopped,reason="signal-received",signal-name="SIGSEGV",signal-meaning="Segmentation fault",thread-id="1",frame={addr="0x7c919994",func="towlower",args=[],from="C:\\WINDOWS\\system32\\ntdll.dll"}
input:31info shared
input:32-stack-list-arguments 2 0 0
input:33-stack-list-locals 2
input:34-stack-list-frames
input:35-thread-list-ids
input:36-data-list-register-values x
10:04:19.890
3) MSalters: I'm not sure what you mean with a "global with class type". The file that is giving the problems have been included in a different DLL in which it worked fine and the DLL loaded successfully.
This is the top of the MatrixVariable.h file:
#include "QtSF/Variable.h" // Located in depending DLL (the DLL in which this file always lived.
#include "Matrix.h" // File located in this DLL
#include "QList" // These are all files from the Qt Framework
#include "QModelIndex"
#include "QItemSelection"
#include "QObject"
using namespace Zenautics;
using namespace std;
class MatrixVariable : public Variable
{
Q_OBJECT
Q_PROPERTY(int RowCount READ rowCount WRITE setRowCount)
Q_PROPERTY(int ColumnCount READ columnCount WRITE setColumnCount)
Q_PROPERTY(int UndoPoints READ undoPoints WRITE setUndoPoints)
public:
//! Default constructor.
MatrixVariable(const QString& name, int rows, int cols, double fill_real = 0, double fill_complex = 0, bool isReal = true);
etc. etc. etc.
A possible solution is to put the MatrixVariable file back in the original DLL but that defeats the whole idea of splitting the DLL into smaller parts which is not really a option.
I get that error from GetLastError() when I fail to load a DLL from a command line EXE recently. It used to work, then I added some MFC code to the DLL. Now all bets are off.
I just had this exact same problem. A dll that had been working just fine, suddenly stopped working. I was taking an access violation in the CRT stuff that initializes static objects. Doing a rebuild all did not fix the problem. But when I manually commented out all the statics, the linker complained about a corrupt file. Link again: Worked. Now I can LoadLibrary. Then, one by one, I added the statics back in. Each time, I recompiled and tested a LoadLibrary. Each time it worked fine. Eventually, all my statics were back, and things working normally.
If I had to guess, some intermediate file used by the linker was corrupted (I see the ilk files constantly getting corrupted by link.exe). If you can, maybe wipe out all your files and do a clean build? But I'm guessing you've already figured things out since this is 6 months old ...