Returning variables in parameters in C++ - c++

Question

I'm not great at C/C++ and I'm trying to write a function that returns console output like "dir". I am returning the exit code as the main return of the function. I pass the command line as one of the arguments as well as two other variables that I am wanting to store stdout and stderr inside of. The information appears to be getting stored in the variables but it looks like the information is destroyed before I can return it. All I'm looking for is information on returning the info in the variables I have passed. I am sure that the code I post will be awful. Ignore that for now, please. Most of my C/C++ coding isn't usually this extensive and is limited to numbers rather than strings.
std::string ReplaceAll(std::string str, const std::string& from, const std::string& to){
size_t start_pos = 0;
while((start_pos = str.find(from, start_pos)) != std::string::npos) {
str.replace(start_pos, from.length(), to);
start_pos += to.length(); // Handles case where 'to' is a substring of 'from'
}
return str;
}
std::string stdoutbuf, stderrbuf = "";
int pipecom(char* cmd, char* qstdout, char* qstderr){
stdoutbuf = "";
stderrbuf = "";
BOOL ok = TRUE;
HANDLE hStdOutPipeRead, hStdOutPipeWrite, hStdReadPipeError, hStdOutPipeError;
SECURITY_ATTRIBUTES sa = {};
sa.nLength = sizeof(SECURITY_ATTRIBUTES);
sa.lpSecurityDescriptor = 0;
sa.bInheritHandle = 1;
if(CreatePipe(&hStdOutPipeRead, &hStdOutPipeWrite, &sa, 0) == FALSE){
return -1;
}
STARTUPINFO si = {};
si.cb = sizeof(STARTUPINFO);
si.dwFlags = STARTF_USESTDHANDLES;
si.hStdError = hStdOutPipeError;
si.hStdOutput = hStdOutPipeWrite;
si.hStdInput = NULL;
PROCESS_INFORMATION procinfo = {};
LPSTR lpApplicationName = NULL;
LPSECURITY_ATTRIBUTES lpProcessAttributes = NULL;
LPSECURITY_ATTRIBUTES lpThreadAttributes = NULL;
char * fullcmd = (char *) malloc(1 + strlen(cmd) + strlen((LPSTR)"cmd /c "));
strcpy(fullcmd, (LPSTR)"cmd /c");
strcat(fullcmd, cmd);
LPSTR lpCommandLine = (LPSTR)fullcmd;
BOOL bInheritHandles = TRUE;
DWORD dwCreationFlags = CREATE_NO_WINDOW;
LPSTR lpEnvironment = NULL;
LPSTR lpCurrentDirectory = NULL;
ok = CreateProcess(lpApplicationName, lpCommandLine, lpProcessAttributes, lpThreadAttributes, bInheritHandles, dwCreationFlags, lpEnvironment, lpCurrentDirectory, &si, &procinfo);
if(ok == FALSE){
return -1;
}
CloseHandle(hStdOutPipeWrite);
CloseHandle(hStdOutPipeError);
char buf[4096+1] = {};
DWORD dwRead = 0;
while((ReadFile(hStdOutPipeRead, &buf, 4096, &dwRead, NULL) != 0) && (dwRead > 0)){
buf[dwRead] = '\0';
stdoutbuf.append(buf);
}
memset(buf, 0, 4096+1);
dwRead = 0;
while((ReadFile(hStdReadPipeError, &buf, 4096, &dwRead, NULL) !=0) && (dwRead > 0)){
buf[dwRead] = '\0';
stderrbuf.append(buf);
}
DWORD exit_code, ex_stat;
if(WaitForSingleObject(procinfo.hProcess, INFINITE) != WAIT_FAILED){
if(GetExitCodeProcess(procinfo.hProcess, &exit_code)){
ex_stat = 1;
}
}
CloseHandle(hStdOutPipeRead);
CloseHandle(hStdReadPipeError);
//this is the area of concern
stdoutbuf = ReplaceAll(stdoutbuf, "\r", "\0");
stderrbuf = ReplaceAll(stderrbuf, "\r", "\0");
qstdout = (char *)malloc(1+strlen(stdoutbuf.c_str()));
qstderr = (char *)malloc(1+strlen(stderrbuf.c_str()));
strcpy(qstdout, stdoutbuf.c_str());
strcpy(qstderr, stderrbuf.c_str());
stdoutbuf.clear();
stderrbuf.clear();
if(ex_stat == 1){
return exit_code;
}
else{
return -1;
}
}

Answer 1

change this
pipecom(char* cmd, char* qstdout, char* qstderr){
to
pipecom(char* cmd, char** qstdout, char** qstderr){
*qstdout = (char *)malloc(1+strlen(stdoutbuf.c_str()));
*qstderr = (char *)malloc(1+strlen(stderrbuf.c_str()));
then dereference and alloc using malloc. otherwise it is just a copy of pointer which will get destroyed once you come out of the function.