How to verify that the `mkfifo` call succeed? - c++

Question

I am new to C++ programming and I am trying to use mkfifo command to create a named pipe that I can read from my java program. Here is my code:
int main(int, char **)
{
std::cout << "START" << std::endl;
int fd;
// FIFO file path
char *myfifo = "/sdcard/tempFifo";
// Creating the named file(FIFO)
// mkfifo(<pathname>, <permission>)
int ret = mkfifo(myfifo, 0666);
std::cout << "mkfifo ret " << ret << std::endl;
std::cout << "errno " << errno << std::endl;
std::cout << "errno str::" << std::strerror(errno) << std::endl;
char arr1[80];
int startCount = 0;
while (1)
{
// Open FIFO for Read only
std::cout << "Opening FIFO.." << std::endl;
fd = open(myfifo, O_RDONLY);
// Read from FIFO
std::cout << "Start reading.." << std::endl;
read(fd, arr1, sizeof(arr1));
if (strcmp(arr1, "start") == 0)
{
if (startCount == 1)
{
std::cout << "Start count is greater than one so exit." << std::endl;
return 0;
}
startCount++;
std::cout << "Start received" << std::endl;
}
sleep(5000);
close(fd);
}
std::cout << "STOP" << std::endl;
return 0;
}
To write "start" on the target pipe, I am using a java code as:
File file = new File("/sdcard/tempFifo");
FileOutputStream fileOutputStream = new FileOutputStream(file);
PrintWriter printWriter = new PrintWriter(fileOutputStream);
printWriter.print("start");
printWriter.flush();
printWriter.close();
I am getting Exception: /sdcard/tempFifo: open failed: ENOENT (No such file or directory) in java applicatoin and when I have executed ls -l /sdcard/tempFifo on adb shell then I am not able to see any tempFifo file on my sdcard of rooted phone.
Does anyone know what is the problem in my code?
Update on errno
mkfifo ret -1
errno 22
errno str::Invalid argument

Answer 1

Android doesn't allow creating pipes on /sdcard so, I have used /system/tempFifo instead of /sdcard/tempFifo to make it work.