im trying to communicate a pthread with a process, using pipes, for a college proyect. i make a struct with the pipes and i pass that structure to the pthread so it can listen on the pipe[0], and on the rest of the code i try to send a string to that running pthread.
Here is my code:
#include <unistd.h>
#include <string>
#include <unistd.h>
#include <stdio.h>
#include <iostream>
#include <pthread.h>
using namespace std;
struct Pipefd{
int pipe[2];
string name;
};
void* listenProcess(void* x){
Pipefd* pf = reinterpret_cast<Pipefd*>(x);
close(0);
dup(pf->pipe[0]);
//here i try to see if the struct i send is ok, but this is not printed.
cout << "pf.name: " << pf->name << endl;
string recive;
while(getline(cin,recive)){
cout << "recive: " << recive << endl;
}
cout << "Problem with getline" << endl;
}
int main(int argc, char *argv[]) {
Pipefd myPipe;
myPipe.name = "Test";
pipe(myPipe.pipe);
void* test = reinterpret_cast<void*>(&myPipe);
pthread_t tid;
pthread_create(&tid,NULL, &listenProcess,test);
close(1);
dup(myPipe.pipe[1]);
cout << "This is a message" << endl;
pthread_join(tid,NULL);
}
if someone can reply me with some ideas of how to make this work it would be awesome, if not, thank you for your time.
Related
I know there is one in C, Sleep(ms), but is there one for C++? I am trying to return an error, then print to the console, then sleep enough for the user to read it before returning the errorcode. Code in C would be:
#include <stdio.h>
#include <windows.h>
int main (int argc, const char *argv[]) {
char *err = "Have an error!";
printf("Error: %s. Program terminating in 5 seconds...", err);
Sleep(5000);
return 1;
}
You could include <windows.h> and just call the WinApi function Sleep just as you would from C. This is mostly pure C++ :
#include <iostream>
#include <string>
#include <chrono>
#include <thread>
using namespace std;
int main (int argc, const char *argv[]) {
string err = "Have an error!";
cout << "Error: " << err << ". Program terminating in 5 seconds..." << endl;
std::chrono::milliseconds timespan(5000);
std::this_thread::sleep_for(timespan);
return 1;
}
I am learning C++ [Java background fwiw] and trying to write a UNIX shell as a project. I am running into a funny little problem with tokenizing the input for execution. The tok function is getting called twice and I'm not sure why. My current test code is the following:
#include <iostream>
#include <vector>
#include <sstream>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/types.h>
using namespace std;
void tok(string, char**);
int main(){
const char* EXIT = "exit";
string input;
cout << "shell>> ";
getline(cin, input);
pid_t pid = fork();
char* args[64]; //arbitrary size, 64 possible whitespace-delimited tokens in command
tok(input, args);
return 0;
}
//copied from http://stackoverflow.com/questions/14265581/parse-split-a-string-in-c-using-string-delimiter-standard-c
void tok(string inStr, char** args){
int last = 0, next = 0, i = 0;
while( (next = inStr.find(' ', last)) != -1){
cout << i++ << ": " << inStr.substr(last, next-last) << endl;
*args++ = strdup(inStr.substr(last, next-last).c_str());
last = next + 1;
}
cout << i++ << ": " << inStr.substr(last) << endl;
*args++ = strdup(inStr.substr(last).c_str());
*args = '\0';
cout << "done tokenizing..." << endl;
}
My output when I actually run the program is:
$ ./a.out
shell>> ls -l
0: ls
1: -l
done tokenizing...
0: ls
1: -l
done tokenizing...
I'm not sure why it would do that. Can anyone guide me in the right direction please? Thank you
The fork function returns twice, once in the original process and once in the newly-created, forked process. Both of those processes then call tok.
There doesn't seem to be any clear reason why you called fork. So the fix may be as simple as eliminating the call to fork.
When you call fork, you create two processes. Each process has nearly the exact same state except for the respective pid_t you receive. If that value is greater than 0, then you are in the parent process (main), and otherwise you are in the child (or fork failed).
Without performing a check on the returned pid_t, both processes will call tok, resulting in the double call behavior you witnessed.
Hide the call behind a check on pid like so:
pid_t pid = fork();
if (pid > 0) // have parent process call tok
{
char* args[64]; //arbitrary size, 64 possible whitespace-delimited tokens in command
tok(input, args);
}
To see what else parent and child processes have in common (or not): check the docs
following code may work fine
#include <iostream>
#include <vector>
#include <sstream>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/types.h>
using namespace std;
void tok(string, char**);
int main(){
const char* EXIT = "exit";
string input;
cout << "shell>> ";
getline(cin, input);
// pid_t pid = fork();
char* args[64];
tok(input, args);
return 0;
}
void tok(string inStr, char** args){
int last = 0, next = 0, i = 0;
while( (next = inStr.find(' ', last)) != -1){
cout << i++ << ": " << inStr.substr(last, next-last) << endl;
*args++ = strdup(inStr.substr(last, next-last).c_str());
last = next + 1;
}
cout << i++ << ": " << inStr.substr(last) << endl;
*args++ = strdup(inStr.substr(last).c_str());
*args = '\0';
cout << "done tokenizing..." << endl;
}
I'm trying to port a program from Windows to Linux.
I encountered a problem when I found out that there isn't a "real" ReadProcessMemory counterpart on Linux; I searched for an alternative and I found ptrace, a powerful process debugger.
I quickly coded two small console applications in C++ to test ptrace, before using it in the program.
TestApp
This is the tracee; it keeps printing two integers every 50 milliseconds while increasing their value by 1 every time.
#include <QCoreApplication>
#include <QThread>
#include <iostream>
using namespace std;
class Sleeper : public QThread
{
public:
static void usleep(unsigned long usecs){QThread::usleep(usecs);}
static void msleep(unsigned long msecs){QThread::msleep(msecs);}
static void sleep(unsigned long secs){QThread::sleep(secs);}
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
int value = 145;
int i = 0;
do {
cout << "i: " << i << " " << "Value: " << value << endl;
value++;
i++;
Sleeper::msleep(50);
} while (true);
return a.exec();
}
MemoryTest
This is the tracer; it asks for the process name and retrieves the PID using the command pidof -s, then ptrace attaches to the process and retrieves the memory address' value every 500 milliseconds, for 10 times.
#include <QCoreApplication>
#include <QThread>
#include <iostream>
#include <string>
#include <sys/ptrace.h>
#include <errno.h>
using namespace std;
class Sleeper : public QThread
{
public:
static void usleep(unsigned long usecs){QThread::usleep(usecs);}
static void msleep(unsigned long msecs){QThread::msleep(msecs);}
static void sleep(unsigned long secs){QThread::sleep(secs);}
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
char process_name[50];
cout << "Process name: ";
cin >> process_name;
char command[sizeof(process_name) + sizeof("pidof -s ")];
snprintf(command, sizeof(command), "pidof -s %s", process_name);
FILE* shell = popen(command, "r");
char pidI[sizeof(shell)];
fgets(pidI, sizeof(pidI), shell);
pclose(shell);
pid_t pid = atoi(pidI);
cout << "The PID is " << pid << endl;
long status = ptrace(PTRACE_ATTACH, pid, NULL, NULL);
cout << "Status: " << status << endl;
cout << "Error: " << errno << endl;
unsigned long addr = 0x012345; // Example address, not the true one
int i = 0;
do {
status = ptrace(PTRACE_PEEKDATA, pid, addr, NULL);
cout << "Status: " << status << endl;
cout << "Error: " << errno << endl;
i++;
Sleeper::msleep(500);
} while (i < 10);
status = ptrace(PTRACE_DETACH, pid, NULL, NULL);
cout << "Status: " << status << endl;
cout << "Error: " << errno << endl;
return a.exec();
}
Everything works fine, but TestApp is paused (SIGSTOP) until ptrace detaches from it.
Also, when it attaches to the process, the status is 0 and the error is 2; the first time it tries to retrieve the memory address value it fails with status -1 and error 3. Is it normal?
Is there a way to prevent ptrace from sending the SIGSTOP signal to the process?
I already tried using PTRACE_SEIZE instead of PTRACE_ATTACH, but it doesn't work: status -1 and error 3.
Update: Using Sleeper in MemoryTest before the "do-while" loop fixes the problem of the first memory address value retrieval, even if the value of seconds, milliseconds or microseconds is 0. Why?
After a lot of research I'm pretty sure that there isn't a way to use ptrace without stopping the process.
I found a real ReadProcessMemory counterpart, called process_vm_readv, which is much more simple.
I'm posting the code in the hope of helping someone who is in my (previous) situation.
Many thanks to mkrautz for his help coding MemoryTest with this beautiful function.
#include <QCoreApplication>
#include <QThread>
#include <sys/uio.h>
#include <stdint.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <iostream>
using namespace std;
class Sleeper : public QThread
{
public:
static void usleep(unsigned long usecs){QThread::usleep(usecs);}
static void msleep(unsigned long msecs){QThread::msleep(msecs);}
static void sleep(unsigned long secs){QThread::sleep(secs);}
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
char process_name[50];
cout << "Process name: ";
cin >> process_name;
char command[sizeof(process_name) + sizeof("pidof -s ")];
snprintf(command, sizeof(command), "pidof -s %s", process_name);
FILE* shell = popen(command, "r");
char pidI[sizeof(shell)];
fgets(pidI, sizeof(pidI), shell);
pclose(shell);
pid_t pid = atoi(pidI);
cout << "The PID is " << pid << endl;
if (pid == 0)
return false;
struct iovec in;
in.iov_base = (void *) 0x012345; // Example address, not the true one
in.iov_len = 4;
uint32_t foo;
struct iovec out;
out.iov_base = &foo;
out.iov_len = sizeof(foo);
do {
ssize_t nread = process_vm_readv(pid, &out, 1, &in, 1, 0);
if (nread == -1) {
fprintf(stderr, "error: %s", strerror(errno));
} else if (nread != in.iov_len) {
fprintf(stderr, "error: short read of %li bytes", (ssize_t)nread);
}
cout << foo << endl;
Sleeper::msleep(500);
} while (true);
return a.exec();
}
Davide,
Have you had a look at the /proc filesystem? It contains memory map files that can be used to peek at the full process space. You can also write in the space to set a breakpoint. There is a wealth of other information in /proc as well.
The PTRACE_CONT command can be used to continue a process. Generally, the target will be paused with a PTRACE_ATTACH when the debugger attaches.
The man page says PTRACE_SIEZE should not pause the process. What flavor and version of Linux are you using? PTRACE_SIEZE has been around for quite awhile so I'm not sure why you are having trouble there.
I note the addr value is set to 0x12345. Is this a valid address in the target space? Or was that just an example? How is the stack address of interest (&value) communicated between the two processes?
I'm not too sure about the return codes. Generally a 0 means all is well, the errno may just be a hangover value from the last error.
--Matt
My program checks for uppercase letters in German language.
#include <iostream>
#include <boost/algorithm/string/classification.hpp>
#include <boost/locale.hpp>
using namespace std;
int main()
{
locale::global(locale("Germany_german"));
//locale::global(locale("de_DE.UTF-8")); //Also tried "de_DE.UTF-8", but does not work
string str1 = "über";
cout << boolalpha << any_of(str1.begin(), str1.end(), boost::algorithm::is_upper()) << endl;
string str2 = "Ää";
cout << boolalpha << any_of(str2.begin(), str2.end(), boost::algorithm::is_upper()) << endl;
return 0;
}
program crashes with error on console
terminate called after throwing an instance of 'std::runtime_error'
what(): locale::facet::_S_create_c_locale name not valid
I don't know what that exact locale string is, "de_DE.UTF-8" doesn't work as well.
Is there any way I can get exact locale name strings for all locales supported by OS. May be there is a list somewhere in header files, but I don't see anything <locale> header.
I wrote a program to print all supported locale names.
#include <Windows.h>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <ostream>
#include <iterator>
using namespace std;
vector<wstring> locals;
BOOL CALLBACK MyFuncLocaleEx(LPWSTR pStr, DWORD dwFlags, LPARAM lparam)
{
locals.push_back(pStr);
return TRUE;
}
int _tmain(int argc, _TCHAR* argv[])
{
EnumSystemLocalesEx(MyFuncLocaleEx, LOCALE_ALL, NULL, NULL);
for (vector<wstring>::const_iterator str = locals.begin(); str != locals.end(); ++str)
wcout << *str << endl;
wcout << "Total " << locals.size() << " locals found." << endl;
return 0;
}
Works great.
...
de
de-AT
de-CH
de-DE
de-DE_phoneb
de-LI
de-LU
...
Total 429 locals found.
#user1 The following might do the same as your elegant code. I can't test it because of the C1189 compiler error.
#include <Winnls.h>
#include <iostream>
#include <ostream>
using namespace std;
int size = 0;
BOOL CALLBACK MyFuncLocaleEx(LPWSTR pStr, DWORD dwFlags, LPARAM lparam) {
size++;
wcout << *pStr << endl;
}
int _tmain(int argc, _TCHAR* argv[])
{
EnumSystemLocalesEx(MyFuncLocaleEx, LOCALE_ALL, NULL, NULL);
wcout << "Total " << size << " locales found." << endl;
return 0;
}
I'm making my first multithreaded program and having some issues. I based the code on an example I found online, which worked fine until I made my changes. The main function below makes several threads which run another function. That function runs instances of another c++ program that I wrote which works fine. The issue is that after the program creates all the threads, it stops running. The other threads continue to run and work fine, but the main thread stops, not even printing out a cout statement I gave it. For example, if I run it the output is:
Enter the number of threads:
// I enter '3'
main() : creating thread, 0
this line prints every time
main() : creating thread, 1
this line prints every time
main() : creating thread, 2
this line prints every time
this is followed by all the output from my other program, which is running 3 times. But the main function never prints out "This line is never printed out". I'm sure there is some fundamental misunderstanding I have of how threads work.
#include <iostream>
#include <stdlib.h>
#include <cstdlib>
#include <pthread.h>
#include <stdio.h>
#include <string>
#include <sstream>
#include <vector>
#include <fstream>
#include <unistd.h>
using namespace std;
struct thread_data{
int thread_id;
};
void *PrintHello(void *threadarg)
{
struct thread_data *my_data;
my_data = (struct thread_data *) threadarg;
stringstream convert;
convert << "./a.out " << my_data->thread_id << " " << (my_data->thread_id+1) << " " << my_data->thread_id;
string sout = convert.str();
system(sout.c_str());
pthread_exit(NULL);
}
int main ()
{
int NUM_THREADS;
cout << "Enter the number of threads:\n";
cin >> NUM_THREADS;
pthread_t threads[NUM_THREADS];
struct thread_data td[NUM_THREADS];
int i;
for( i=0; i < NUM_THREADS; i++ ){
cout <<"main() : creating thread, " << i << endl;
td[i].thread_id = i;
pthread_create(&threads[i], NULL, PrintHello, (void *)&td[i]);
cout << endl << "this line prints every time" << endl;
}
cout << endl << "This line is never printed out";
pthread_exit(NULL);
}
It's because you're not using pthread_join(threads[i],NULL). pthread_join() prevents the main from ending before the threads finish executing