How to execute commands in the same process - c++

Question

I made my own function to execute a command and save the result. The problem is the command is executed once and I can't execute several commands with the same "context". For example. If I execute cd .., the next command my cd .. will be ignored. This is my code :
std::string executeCommand(const std::string& cmd)
{
system((cmd + " > temp.txt").c_str());
std::ifstream ifs("temp.txt");
std::string ret{ std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>() };
ifs.close(); // must close the inout stream so the file can be cleaned up
return ret;
}
Can I have a sample with this feature ?

Answer 1

Do you use Windows system？
In Windows, you can interact with cmd through a Pipe.
like this:
#define BUFFER_SIZE 131072 //128*1024‬
void work() {
HANDLE hinRead, hinWrite, houtRead, houtWrite;
SECURITY_ATTRIBUTES sa;
sa.nLength = sizeof(sa);
sa.lpSecurityDescriptor = 0;
sa.bInheritHandle = true;
if (!CreatePipe(&hinRead, &hinWrite, &sa, 0)) {
MessageBoxA(NULL, "Error CreatePipe", "Error", MB_ICONERROR);
}
if (!CreatePipe(&houtRead, &houtWrite, &sa, 0)) {
MessageBoxA(NULL, "Error CreatePipe", "Error", MB_ICONERROR);
}
STARTUPINFOA si;
ZeroMemory(&si, sizeof(si));
si.dwFlags = STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
si.wShowWindow = SW_HIDE;
si.hStdInput = hinRead;//redirect Input
si.hStdOutput = si.hStdError = houtWrite;//redirect Output
PROCESS_INFORMATION ProcessInformation;
char cmdLine[256] = { 0 };
GetSystemDirectoryA(cmdLine, sizeof(cmdLine));
strcat(cmdLine, ("\\cmd.exe"));
if (CreateProcessA(cmdLine, NULL, NULL, NULL, TRUE, 0, NULL, NULL, &si, &ProcessInformation) == 0) {
MessageBoxA(NULL, "Error CreateProcessA", "Error", MB_ICONERROR);
}
char* pbuff = new char[BUFFER_SIZE];
DWORD dw;
Sleep(100);//wait cmd start
ReadFile(houtRead, pbuff, BUFFER_SIZE-1, &dw, NULL);
pbuff[dw] = 0;
printf(pbuff);//version info
while (1) {
char* p = pbuff;
while ((*p = getchar()) != '\n') {
++p;
}
WriteFile(hinWrite, pbuff, p - pbuff + 1, &dw, 0);
while (1) {
ReadFile(houtRead, pbuff, BUFFER_SIZE - 1, &dw, NULL);
pbuff[dw] = 0;
printf("%s", pbuff);
if (pbuff[dw - 1] == '>')break;
}
}
}
Pipe can read/write like a file.
In other systems, there is also something like pipe，but I'm not familiar with them.
edit: another more clear example
int main() {
HANDLE hinRead, hinWrite, houtRead, houtWrite;
SECURITY_ATTRIBUTES sa;
sa.nLength = sizeof(sa);
sa.lpSecurityDescriptor = 0;
sa.bInheritHandle = true;
if (!CreatePipe(&hinRead, &hinWrite, &sa, 0)) {
MessageBoxA(NULL, "Error CreatePipe", "Error", MB_ICONERROR);
}
if (!CreatePipe(&houtRead, &houtWrite, &sa, 0)) {
MessageBoxA(NULL, "Error CreatePipe", "Error", MB_ICONERROR);
}
STARTUPINFOA si;
ZeroMemory(&si, sizeof(si));
si.dwFlags = STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
si.wShowWindow = SW_HIDE;//no window
si.hStdInput = hinRead;//redirect Input
si.hStdOutput = si.hStdError = houtWrite;//redirect Output
PROCESS_INFORMATION pi;
char cmdLine[256] = { 0 };
GetSystemDirectoryA(cmdLine, sizeof(cmdLine));
strcat(cmdLine, ("\\cmd.exe"));
if (CreateProcessA(cmdLine, NULL, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi) == 0) {
MessageBoxA(NULL, "Error CreateProcessA", "Error", MB_ICONERROR);
}
Sleep(100);//wait cmd start
char* pbuff = new char[1024 * 128];
DWORD dw;
ReadFile(houtRead, pbuff, 1024 * 128, &dw, NULL), pbuff[dw] = 0, printf("%s", pbuff);//cmd version info
WriteFile(hinWrite, "cd ..\n", 6, &dw, NULL);//send command to cmd.exe
Sleep(100);//wait command execute and cmd outputs
ReadFile(houtRead, pbuff, 1024 * 128, &dw, NULL), pbuff[dw] = 0, printf("%s", pbuff);
WriteFile(hinWrite, "dir\n", 4, &dw, NULL);//another command
Sleep(100);
ReadFile(houtRead, pbuff, 1024 * 128, &dw, NULL), pbuff[dw] = 0, printf("%s", pbuff);
delete[] pbuff;
TerminateProcess(pi.hProcess, 0);//Terminate cmd.exe
return 0;
}