I am looking for a win32 api function that clears the console, much like the cls command
Thanks!
Devjeet
This is pretty old, but should still work. Conversion to assembly language is left as an exercise for the reader, but shouldn't be terribly difficult (most of it is just function calls, and the multiplication is trivial):
#include <windows.h>
void clear_screen(char fill = ' ') {
COORD tl = {0,0};
CONSOLE_SCREEN_BUFFER_INFO s;
HANDLE console = GetStdHandle(STD_OUTPUT_HANDLE);
GetConsoleScreenBufferInfo(console, &s);
DWORD written, cells = s.dwSize.X * s.dwSize.Y;
FillConsoleOutputCharacter(console, fill, cells, tl, &written);
FillConsoleOutputAttribute(console, s.wAttributes, cells, tl, &written);
SetConsoleCursorPosition(console, tl);
}
There is no Win32 API which directly clears the console - you need to use something like FillConsoleOutputCharacter.
Related
So my problem sounds like this.
I have some platform dependent code (embedded system) which writes to some MMIO locations that are hardcoded at specific addresses.
I compile this code with some management code inside a standard executable (mainly for testing) but also for simulation (because it takes longer to find basic bugs inside the actual HW platform).
To alleviate the hardcoded pointers, i just redefine them to some variables inside the memory pool. And this works really well.
The problem is that there is specific hardware behavior on some of the MMIO locations (w1c for example) which makes "correct" testing hard to impossible.
These are the solutions i thought of:
1 - Somehow redefine the accesses to those registers and try to insert some immediate function to simulate the dynamic behavior. This is not really usable since there are various ways to write to the MMIO locations (pointers and stuff).
2 - Somehow leave the addresses hardcoded and trap the illegal access through a seg fault, find the location that triggered, extract exactly where the access was made, handle and return. I am not really sure how this would work (and even if it's possible).
3 - Use some sort of emulation. This will surely work, but it will void the whole purpose of running fast and native on a standard computer.
4 - Virtualization ?? Probably will take a lot of time to implement. Not really sure if the gain is justifiable.
Does anyone have any idea if this can be accomplished without going too deep? Maybe is there a way to manipulate the compiler in some way to define a memory area for which every access will generate a callback. Not really an expert in x86/gcc stuff.
Edit: It seems that it's not really possible to do this in a platform independent way, and since it will be only windows, i will use the available API (which seems to work as expected). Found this Q here:
Is set single step trap available on win 7?
I will put the whole "simulated" register file inside a number of pages, guard them, and trigger a callback from which i will extract all the necessary info, do my stuff then continue execution.
Thanks all for responding.
I think #2 is the best approach. I routinely use approach #4, but I use it to test code that is running in the kernel, so I need a layer below the kernel to trap and emulate the accesses. Since you have already put your code into a user-mode application, #2 should be simpler.
The answers to this question may provide help in implementing #2. How to write a signal handler to catch SIGSEGV?
What you really want to do, though, is to emulate the memory access and then have the segv handler return to the instruction after the access. This sample code works on Linux. I'm not sure if the behavior it is taking advantage of is undefined, though.
#include <stdint.h>
#include <stdio.h>
#include <signal.h>
#define REG_ADDR ((volatile uint32_t *)0x12340000f000ULL)
static uint32_t read_reg(volatile uint32_t *reg_addr)
{
uint32_t r;
asm("mov (%1), %0" : "=a"(r) : "r"(reg_addr));
return r;
}
static void segv_handler(int, siginfo_t *, void *);
int main()
{
struct sigaction action = { 0, };
action.sa_sigaction = segv_handler;
action.sa_flags = SA_SIGINFO;
sigaction(SIGSEGV, &action, NULL);
// force sigsegv
uint32_t a = read_reg(REG_ADDR);
printf("after segv, a = %d\n", a);
return 0;
}
static void segv_handler(int, siginfo_t *info, void *ucontext_arg)
{
ucontext_t *ucontext = static_cast<ucontext_t *>(ucontext_arg);
ucontext->uc_mcontext.gregs[REG_RAX] = 1234;
ucontext->uc_mcontext.gregs[REG_RIP] += 2;
}
The code to read the register is written in assembly to ensure that both the destination register and the length of the instruction are known.
This is how the Windows version of prl's answer could look like:
#include <stdint.h>
#include <stdio.h>
#include <windows.h>
#define REG_ADDR ((volatile uint32_t *)0x12340000f000ULL)
static uint32_t read_reg(volatile uint32_t *reg_addr)
{
uint32_t r;
asm("mov (%1), %0" : "=a"(r) : "r"(reg_addr));
return r;
}
static LONG WINAPI segv_handler(EXCEPTION_POINTERS *);
int main()
{
SetUnhandledExceptionFilter(segv_handler);
// force sigsegv
uint32_t a = read_reg(REG_ADDR);
printf("after segv, a = %d\n", a);
return 0;
}
static LONG WINAPI segv_handler(EXCEPTION_POINTERS *ep)
{
// only handle read access violation of REG_ADDR
if (ep->ExceptionRecord->ExceptionCode != EXCEPTION_ACCESS_VIOLATION ||
ep->ExceptionRecord->ExceptionInformation[0] != 0 ||
ep->ExceptionRecord->ExceptionInformation[1] != (ULONG_PTR)REG_ADDR)
return EXCEPTION_CONTINUE_SEARCH;
ep->ContextRecord->Rax = 1234;
ep->ContextRecord->Rip += 2;
return EXCEPTION_CONTINUE_EXECUTION;
}
So, the solution (code snippet) is as follows:
First of all, i have a variable:
__attribute__ ((aligned (4096))) int g_test;
Second, inside my main function, i do the following:
AddVectoredExceptionHandler(1, VectoredHandler);
DWORD old;
VirtualProtect(&g_test, 4096, PAGE_READWRITE | PAGE_GUARD, &old);
The handler looks like this:
LONG WINAPI VectoredHandler(struct _EXCEPTION_POINTERS *ExceptionInfo)
{
static DWORD last_addr;
if (ExceptionInfo->ExceptionRecord->ExceptionCode == STATUS_GUARD_PAGE_VIOLATION) {
last_addr = ExceptionInfo->ExceptionRecord->ExceptionInformation[1];
ExceptionInfo->ContextRecord->EFlags |= 0x100; /* Single step to trigger the next one */
return EXCEPTION_CONTINUE_EXECUTION;
}
if (ExceptionInfo->ExceptionRecord->ExceptionCode == STATUS_SINGLE_STEP) {
DWORD old;
VirtualProtect((PVOID)(last_addr & ~PAGE_MASK), 4096, PAGE_READWRITE | PAGE_GUARD, &old);
return EXCEPTION_CONTINUE_EXECUTION;
}
return EXCEPTION_CONTINUE_SEARCH;
}
This is only a basic skeleton for the functionality. Basically I guard the page on which the variable resides, i have some linked lists in which i hold pointers to the function and values for the address in question. I check that the fault generating address is inside my list then i trigger the callback.
On first guard hit, the page protection will be disabled by the system, but i can call my PRE_WRITE callback where i can save the variable state. Because a single step is issued through the EFlags, it will be followed immediately by a single step exception (which means that the variable was written), and i can trigger a WRITE callback. All the data required for the operation is contained inside the ExceptionInformation array.
When someone tries to write to that variable:
*(int *)&g_test = 1;
A PRE_WRITE followed by a WRITE will be triggered,
When i do:
int x = *(int *)&g_test;
A READ will be issued.
In this way i can manipulate the data flow in a way that does not require modifications of the original source code.
Note: This is intended to be used as part of a test framework and any penalty hit is deemed acceptable.
For example, W1C (Write 1 to clear) operation can be accomplished:
void MYREG_hook(reg_cbk_t type)
{
/** We need to save the pre-write state
* This is safe since we are assured to be called with
* both PRE_WRITE and WRITE in the correct order
*/
static int pre;
switch (type) {
case REG_READ: /* Called pre-read */
break;
case REG_PRE_WRITE: /* Called pre-write */
pre = g_test;
break;
case REG_WRITE: /* Called after write */
g_test = pre & ~g_test; /* W1C */
break;
default:
break;
}
}
This was possible also with seg-faults on illegal addresses, but i had to issue one for each R/W, and keep track of a "virtual register file" so a bigger penalty hit. In this way i can only guard specific areas of memory or none, depending on the registered monitors.
Is it possible to determine the demand a non recursive function on the stack without external computation, right in the text of the program? I need this to allocate a memory resource for the thread in very small micro-controllers, such as AVR. And I need know this before function calling. Directive --stack-usage is very non informative, unfortunately. Or I something do not understand?
Getting the address of a passed argument yields it's place on the stack. Therefore running this:
#include <stdio.h>
void my_fun(int dummy);
int get_stack_space(int dummy);
int main(void)
{
int dummy = 0;
my_fun(dummy);
return 0;
}
void my_fun(int dummy)
{
// do stuff
printf("%d\n", get_stack_space((int)&dummy));
return;
}
int get_stack_space(int dummy)
{
return dummy - (int)&dummy;
}
should get you the distance in bytes on the stack between the point of calling my_fun() and calling get_stack_space(). Hope it helps.
Edit: on x86 you get the distance + a machine word for the push of the return address when calling my_fun() + a machine word for the push of ebp at the start of my_fun()
I am using BDS 2006 Turbo C++ for a long time now and some of my bigger projects (CAD/CAM,3D gfx engines and Astronomic computations) occasionally throw an exception (for example once in 3-12 months of 24/7 heavy duty usage). After extensive debugging I found this:
//code1:
struct _s { int i; } // any struct
_s *s=new _s[1024]; // dynamic allocation
delete[] s; // free up memory
this code is usually inside template where _s can be also class therefore delete[] this code should work properly, but the delete[] does not work properly for structs (classes looks OK). No exceptions is thrown, the memory is freed, but it somehow damages the memory manager allocation tables and after this any new allocation can be wrong (new can create overlapped allocations with already allocated space or even unallocated space hence the occasional exceptions)
I have found that if I add empty destructor to _s than suddenly seems everything OK
struct _s { int i; ~_s(){}; }
Well now comes the weird part. After I update this to my projects I have found that AnsiString class has also bad reallocations. For example:
//code2:
int i;
_s *dat=new _s[1024];
AnsiString txt="";
// setting of dat
for (i=0;i<1024;i++) txt+="bla bla bla\r\n";
// usage of dat
delete[] dat;
In this code dat contains some useful data, then later is some txt string created by adding lines so the txt must be reallocated few times and sometimes the dat data is overwritten by txt (even if they are not overlapped, I thing the temp AnsiString needed to reallocate txt is overlapped with dat)
So my questions are:
Am I doing something wrong in code1, code2 ?
Is there any way to avoid AnsiString (re)allocation errors ? (but still using it)
After extensive debugging (after posting question 2) I have found that AnsiString do not cause problems. They only occur while using them. The real problem is probably in switching between OpenGL clients. I have Open/Save dialogs with preview for vector graphics. If I disable OpenGL usage for these VCL sub-windows than AnsiString memory management errors disappears completely. I am not shore what is the problem (incompatibility between MFC/VCL windows or more likely I made some mistake in switching contexts, will further investigate). Concern OpenGL windows are:
main VCL Form + OpenGL inside Canvas client area
child of main MFC Open/Save dialog + docked preview VCL Form + OpenGL inside Canvas client area
P.S.
these errors depend on number of new/delete/delete[] usages not on the allocated sizes
both code1 and code2 errors are repetitive (for example have a parser to load complex ini file and the error occurs on the same line if the ini is not changed)
I detect these errors only on big projects (plain source code > 1MB) with combined usage of AnsiString and templates with internal dynamic allocations, but is possible that they are also in simpler projects but occurs so rarely that I miss it.
Infected projects specs:
win32 noinstall standalone (using Win7sp1 x64 but on XPsp3 x32 behaves the same)
does not meter if use GDI or OpenGl/GLSL
does not meter if use device driver DLLs or not
no OCX,or nonstandard VCL component
no DirectX
1 Byte aligned compilation/link
do not use RTL,packages or frameworks (standalone)
Sorry for bad English/grammar ...
any help / conclusion / suggestion appreciated.
After extensive debugging i finely isolated the problem.
Memory management of bds2006 Turbo C++ became corrupt after you try to call any delete for already deleted pointer. for example:
BYTE *dat=new BYTE[10],*tmp=dat;
delete[] dat;
delete[] tmp;
After this is memory management not reliable. ('new' can allocate already allocated space)
Of course deletion of the same pointer twice is bug on programmers side, but i have found the real cause of all my problems which generates this problem (without any obvious bug in source code) see this code:
//---------------------------------------------------------------------------
class test
{
public:
int siz;
BYTE *dat;
test()
{
siz=10;
dat=new BYTE[siz];
}
~test()
{
delete[] dat; // <- add breakpoint here
siz=0;
dat=NULL;
}
test& operator = (const test& x)
{
int i;
for (i=0;i<siz;i++) if (i<x.siz) dat[i]=x.dat[i];
for ( ;i<siz;i++) dat[i]=0;
return *this;
}
};
//---------------------------------------------------------------------------
test get()
{
test a;
return a; // here call a.~test();
} // here second call a.~test();
//---------------------------------------------------------------------------
void main()
{
get();
}
//---------------------------------------------------------------------------
In function get() is called destructor for class a twice. Once for real a and once for its copy because I forget to create constructor
test::test(test &x);
[Edit1] further upgrades of code
OK I have refined the initialization code for both class and struct even templates to fix even more bug-cases. Add this code to any struct/class/template and if needed than add functionality
T() {}
T(const T& a) { *this=a; }
~T() {}
T* operator = (const T *a) { *this=*a; return this; }
//T* operator = (const T &a) { ...copy... return this; }
T is the struct/class name
the last operator is needed only if T uses dynamic allocations inside it if no allocations are used you can leave it as is
This also resolves other compiler issues like this:
Too many initializers error for a simple array in bcc32
If anyone have similar problems hope this helps.
Also look at traceback a pointer in c++ code mmap if you need to debug your memory allocations...
I am not a native C++ programmer, so I need some help with the following:
I got this code working:
#pragma comment(lib, "winmm.lib")
LPCWSTR openCDCommand = L"set cdaudio door open";
//comes from Windows.h, needs winmm.lib see header includes
int errCode = mciSendString(openCDCommand, 0, 0, 0);
Questions:
Do I need to work with LPCWSTR? Why didn't I find a System::String example?
How should I handle 'string concatination'? I cant simply do L"foo"+L"baar"?
Am I on the totally wrong way to play sounds with mciSendString? (actually I really want to use MCI Command and MCI sendString as i did in other projects before)
Is there another way to include the external function mciSendString so it can handle handles?
The signature of mciSendString is
MCIERROR mciSendString(
LPCTSTR lpszCommand,
LPTSTR lpszReturnString,
UINT cchReturn,
HANDLE hwndCallback);
So, regarding the first 2 parameters, in unicode it will be a wchar pointer and in multibyte it will be a char pointer. It's the signature. You cannot change that and you shouldn't worry about that.
std::wstring someString( L"Foo" );
someString.append( L"bar ");
I would play sound with core audio API, waveOut or maybe DirectSound. But, not with the mciSendString().
I'm afraid I don't understand this one.. can you explain it better?
This now works for me - took some time, but maybe in future this will help others:
#include "vcclr.h" // compile with /clr(!)
int Player::mciSendStringHandle(String ^ givenHandle)
{
pin_ptr<const wchar_t> wch = PtrToStringChars(givenHandle);
return mciSendString(wch, 0, 0, 0);
}
I need to change reference of a function in a Mac OS process at runtime to a custom function defined in my own custom dylib. I kept the new function signature same as the original.
For example I need to change "open" function to "myopen" function.
I tried processing __LINKEDIT segment to get the dynamic symbol table and string table.
I used following pointers,
1. the VMAddrress from __LINKEDIT segment,
2. mach_header and vmaddr_slide from the "_dyld_register_func_for_add_image" callback,
3. symoff and stroff from symtab_command.
But I am unable to get the symbol table and string table mentioned in the __LINKEDIT segment.
Can someone throw some light on this?
Thanks in advance.
If the function in question is a library function, and not statically compiled into the executable, you don't need to do any of that - you can use function interposing, instead. Specifically, add this to your library:
// The attribute creates a Mach-O Section in your library - q.v. libgmalloc.dylib for
// a nice example
static const interpose_t interposing_functions[] \
__attribute__ ((section("__DATA, __interpose"))) = {
{ (void *)my_open, (void *)open },
{ (void *)my_close, (void *)close }, // .. etc
};
int my_open(const char *path, int flags, mode_t mode)
{
int rc;
// Prolog - do something before open
rc = open(path, flags, mode); // call real open
// Epilog - record rc, etc..
return rc;
}
There are several excellent books on OS X internals which can provide you with samples, though apparently according to S.O site policies we can't link you to them. That said, the above code snippet should work. Bear in mind, that this won't work on calls to open performed by other dylibs (though there are more complicated ways to get that, as well)