Cannot read from anonymous pipe - c++

Question

I began to study the anonymous pipe in windows and ran into a problem.
The program should create a child process that will handle the commands given ones to enter. But I can not read from the pipe until the child process works.
Here is the programm
#define _CRT_SECURE_NO_DEPRECATE
#include "windows.h"
#include "cstdio"
#include "tchar.h"
#include "io.h"
#include "conio.h"
#include "cstring"
static const int bufSize = 20;
int main() {
STARTUPINFO si;
PROCESS_INFORMATION pi;
LPTSTR szCmdline = _tcsdup(TEXT("Project2\\Release\\command_handler.exe"));
HANDLE writePipe, readPipe, writePipeInput, readPipeInput;
SECURITY_ATTRIBUTES sa;
ZeroMemory(&si, sizeof(STARTUPINFO));
si.cb = sizeof(STARTUPINFO);
sa.nLength = sizeof(SECURITY_ATTRIBUTES);
sa.lpSecurityDescriptor = NULL;
sa.bInheritHandle = TRUE;
if(!CreatePipe(&readPipe, &writePipe, &sa, 0) || !CreatePipe(&readPipeInput, &writePipeInput, &sa, 0))
{
printf("ERROR: cannot create pipe\n");
system("pause");
exit(1);
}
si.dwFlags = STARTF_USESTDHANDLES;
si.hStdOutput = writePipe;
si.hStdInput = readPipeInput;
DWORD dwByteRead, dwByteWrite;
if(!CreateProcess(0, szCmdline, 0, 0, TRUE, CREATE_NO_WINDOW, 0, 0, &si, &pi)) {
printf("ERROR: cannot create process\n");
system("pause");
exit(2);
}
CloseHandle(writePipe);
CloseHandle(readPipeInput);
printf("Procces ready!\n");
TQueue <int> q;
TQueue <int> tmp;
char c;
char s[bufSize];
int value;
for ( ; ; ) {
int i;
for(i = 0;i < bufSize && (s[i] = getchar()) != '\n';++i);
WriteFile(writePipeInput,s,i + 1,&dwByteWrite,NULL);
ReadFile(readPipe, &c, (int)1, &dwByteRead, NULL);
printf("Get : '%c'\n",c);
switch (c) {
case '+':
ReadFile(readPipe, &value, sizeof(int), &dwByteRead, NULL);
printf("%d\n",value);
q.push(value);
printf("OK\n");
break;
case '-':
if (!q.empty()) {
q.pop();
}
printf("OK\n");
break;
case 'f':
if (!q.empty()) {
printf("%d\nOK\n",q.firstEl());
} else {
printf("Queue is empty\nOK\n");
}
break;
case 'p':
if (q.empty()) {
printf("empty");
}
while (!q.empty()) {
tmp.push(q.firstEl());
printf("%d ",q.firstEl());
q.pop();
}
printf("\nOK\n");
while (!tmp.empty()) {
q.push(tmp.firstEl());
tmp.pop();
}
break;
case 'e':
printf("%s\nOK\n",q.empty()?"yes!":"no");
break;
case 'q':
break;
case '?':
printf("ERROR: undefined command\n");
break;
default:
printf("Fatal error: wrong symbol from hadeler '%c'\n",c);
//system("pause");
//exit(3);
}
if (c == 'q') break;
}
CloseHandle(readPipe);
CloseHandle(writePipeInput);
printf("Exited normaly\n");
system("pause");
}
And this is handler
#define _CRT_SECURE_NO_DEPRECATE
#include <stdio.h>
#include <string.h>
static const int sz = 10;
char read_cmd(char *s) {
char c = getchar();
int i;
for (i = 0;(i < sz) && (c != ' ') && (c != '\n');i++) {
s[i] = c;
c = getchar();
// printf("%c",s[i]);
}
s[i] = '\0';
return c;
}
char correct(char res) {
if (res != '\n') {
while (getchar() != '\n');
return 0;
}
return 1;
}
int main() {
char s[sz + 1];
char c, res;
int val = 0;
for ( ; ; ) {
res = read_cmd(s);
if (strcmp(s,"add") == 0) {
val = 0;
while ((c = getchar()) >= '0' && c <= '9') {
val = val * 10 + c - '0';
}
res = c;
c = '+';
}else if (strcmp(s,"pop") == 0) {
c = '-';
}else if (strcmp(s,"first") == 0) {
c = 'f';
}else if (strcmp(s,"print") == 0) {
c = 'p';
}else if (strcmp(s,"empty") == 0) {
c = 'e';
}else if (strcmp(s,"help") == 0) {
c = 'h';
}else if (strcmp(s,"quit") == 0) {
c = 'q';
}else {
c = '?';
}
if (!correct(res)) c = '?';
printf("%c",c);
if (c == 'q') break;
if (c == '+') printf("%d",val);
}
return 0;
}
So if I run it and immediately type "quit" it works, otherwise it stop when trying get result from output pipe.
Why is this happening?
Thanks in advance for your reply.

Answer 1

I rewrote the program again and it worked. Honestly, I do not know that there was not correct. Here is a working version:
#define _CRT_SECURE_NO_DEPRECATE
#include <windows.h>
#include <stdio.h>
#define BUFSIZE 256
template <class T> class TQueue {
private:
class TQueEl {
public:
T value;
TQueEl *next, *prev;
};
TQueEl *first, *last;
int size;
public:
int& operator = (TQueue <T>& b){
while (!empty ()) {
pop ();
}
while (!b.empty ()) {
push(b.firstEl ());
b.pop ();
}
}
TQueue () {
size = 0;
first = last = nullptr;
}
void push (T val) {
if (size == 0) {
first = last = new TQueEl;
first -> next = first -> prev = nullptr;
first -> value = val;
} else {
last -> next = new TQueEl;
last -> next -> prev = last;
last = last -> next;
last -> next = nullptr;
last -> value = val;
}
size++;
}
T firstEl () {
return first -> value;
}
void pop () {
TQueEl *tmp=first;
if (size == 1) {
first = last = nullptr;
}
else if ( empty() ) {
// error("pop of empty queue");
}
else {
first = first -> next;
first -> prev = nullptr;
}
size--;
delete tmp;
}
bool empty () {
return !size;
}
~TQueue () {
TQueEl *tmp;
while (first != nullptr) {
tmp = first;
first = first -> next;
delete tmp;
}
}
};
DWORD WINAPI rerout(LPVOID params) {
DWORD dwByteWrite, dwByteRead;
char buffer[BUFSIZE];
HANDLE hParentStdIn = GetStdHandle(STD_INPUT_HANDLE);
HANDLE childInput = (HANDLE) params;
for ( ; ; ) {
ReadFile(hParentStdIn, buffer, BUFSIZE, &dwByteRead, NULL);
WriteFile(childInput, buffer, dwByteRead, &dwByteWrite, NULL);
}
return 0;
}
int main() {
HANDLE childInputRd = NULL;
HANDLE childInputWr = NULL;
HANDLE childOutputRd = NULL;
HANDLE childOutputWr = NULL;
SECURITY_ATTRIBUTES sa;
sa.nLength = sizeof(SECURITY_ATTRIBUTES);
sa.bInheritHandle = TRUE;
sa.lpSecurityDescriptor = NULL;
if ( ! CreatePipe(&childOutputRd, &childOutputWr, &sa, 0) ) {
printf("Fatal error: cannot create child output pipe\n");
system("pause");
exit(1);
}
if (! CreatePipe(&childInputRd, &childInputWr, &sa, 0)) {
printf("Fatal error: cannot create child input pipe\n");
system("pause");
exit(2);
}
TCHAR szCmdline[]=TEXT("Project2\\Release\\command_handler.exe");
PROCESS_INFORMATION pi;
STARTUPINFO si;
ZeroMemory( &pi, sizeof(PROCESS_INFORMATION) );
ZeroMemory( &si, sizeof(STARTUPINFO) );
si.cb = sizeof(STARTUPINFO);
si.hStdError = childOutputWr;
si.hStdOutput = childOutputWr;
si.hStdInput = childInputRd;
si.dwFlags = STARTF_USESTDHANDLES;
if ( !CreateProcess(NULL, szCmdline, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi) ) {
printf("Fatal error: cannot create child process\n");
system("pause");
exit(3);
}
else {
CloseHandle(childInputRd);
CloseHandle(childOutputWr);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
}
DWORD reroutThreadID;
HANDLE inputRerouting = CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)rerout,(LPVOID) childInputWr,0 , &reroutThreadID);
if (inputRerouting == NULL) {
printf("Fatal error: cannot create thread\n");
system("pause");
exit (4);
}
TQueue <int> q;
TQueue <int> tmp;
DWORD dwRead;
CHAR c;
HANDLE hParentStdOut = GetStdHandle(STD_OUTPUT_HANDLE);
for (;;) {
ReadFile( childOutputRd, &c, sizeof(char), &dwRead, NULL);
switch (c) {
case '+':
int value;
ReadFile( childOutputRd, &value, sizeof(int), &dwRead, NULL);
q.push(value);
printf("OK\n");
break;
case '-':
if (!q.empty()) {
q.pop();
printf("OK\n");
}
else {
printf("Queue is empty!\n");
}
break;
case 'f':
if (!q.empty()) {
printf("%d\n",q.firstEl());
} else {
printf("Queue is empty!\n");
}
break;
case 'p':
printf("\n>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\n\n");
if (q.empty()) {
printf("empty");
}
while (!q.empty()) {
tmp.push(q.firstEl());
printf("%d ",q.firstEl());
q.pop();
}
while (!tmp.empty()) {
q.push(tmp.firstEl());
tmp.pop();
}
printf("\n\n<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<\n\nOK\n");
break;
case 'e':
printf("%s\n",q.empty()?"YES":"NO");
break;
case 'q':
break;
case '?':
printf("ERROR: undefined command\n");
break;
default:
printf("Fatal error: wrong symbol from hadeler '%c'\n",c);
system("pause");
exit(5);
}
if (c == 'q') break;
}
CloseHandle(inputRerouting);
CloseHandle(childInputWr);
CloseHandle(childOutputRd);
system("pause");
return 0;
}
And the handler:
#define _CRT_SECURE_NO_DEPRECATE
#include <windows.h>
#include <stdio.h>
#define BUFSIZE 5
HANDLE hStdin, hStdout;
DWORD dwRead, dwWritten;
void readCmd(char* s) {
ReadFile(hStdin, s, 1, &dwRead, NULL);
int i;
for (i = 0;(i < BUFSIZE) && (s[i] != ' ') && (s[i] != '\n') && (s[i] != '\r');i++) {
ReadFile(hStdin, s + i + 1, 1, &dwRead, NULL);
}
s[i] = '\0';
}
bool correct() {
char c;
ReadFile(hStdin, &c, sizeof(char), &dwRead, NULL);
if (c != '\n') {
while (c != '\n') ReadFile(hStdin, &c, sizeof(char), &dwRead, NULL);
return 0;
}
return 1;
}
int main() {
hStdout = GetStdHandle(STD_OUTPUT_HANDLE);
hStdin = GetStdHandle(STD_INPUT_HANDLE);
if ( (hStdout == INVALID_HANDLE_VALUE) || (hStdin == INVALID_HANDLE_VALUE) ) {
ExitProcess(1);
}
int val;
char s[BUFSIZE + 1];
char c,digit;
for (;;) {
readCmd(s);
if (strcmp(s,"add") == 0) {
val = 0;
ReadFile(hStdin, &digit, 1, &dwRead, NULL);
if (digit == '\n') {
c = '?';
WriteFile(hStdout,&c,sizeof(char),&dwRead,NULL);
continue;
}
else if (digit < '0' || digit > '9') {
c = '?';
}
else {
c = '+';
}
while (digit >= '0' && digit <= '9') {
val = val * 10 + digit - '0';
ReadFile(hStdin, &digit, 1, &dwRead, NULL);
}
}else if (strcmp(s,"pop") == 0) {
c = '-';
}else if (strcmp(s,"first") == 0) {
c = 'f';
}else if (strcmp(s,"print") == 0) {
c = 'p';
}else if (strcmp(s,"empty") == 0) {
c = 'e';
}else if (strcmp(s,"help") == 0) {
c = 'h';
}else if (strcmp(s,"quit") == 0) {
c = 'q';
}else {
c = '?';
}
if (!correct()) c = '?';
WriteFile(hStdout, &c, 1, &dwRead, NULL);
if (c == 'q') break;
if (c == '+') WriteFile(hStdout, &val, sizeof(int), &dwRead, NULL);
}
return 0;
}
Thank you all for your help!