read was not declared error message - c++

Question

I am cross compiling a package (libqmi).(With simple compiling it was fine.)
The problem came out when I tried to comply a c++ part.
I got the message that is
"read is not declared".
I know it does not need to be included in case of C, but what about C++?
I tried to add the headers by hand: fcntl.h and unistd.h too, without any solution.
(the compiler found them and included, but the error message is still left)
Do you have any idea what the problem can be behind this?
I do not think the problem is wrong, as it is a realised and good with host compiler.
EDIT:
thanks the comments.
host: Linux, x86,
target: Linux, arm
unistd.h header does not solved the problem:
I also tried type alloc, maybe there is misalloc.
GobiQMICore.cpp: In member function 'virtual std::vector, std::basic_string > > cGobiQMICore::GetAvailableDevices()':
GobiQMICore.cpp:319:39: error: 'read' was not declared in this scope
GobiQMICore.cpp:334:21: error: 'close' was not declared in this scope
the code:
/*===========================================================================
METHOD:
GetAvailableQDLPorts (Public Method)
DESCRIPTION:
Return the set of available Gobi QDL ports
RETURN VALUE:
std::vector <sDeviceID>
===========================================================================*/
std::vector <std::string> cGobiQDLCore::GetAvailableQDLPorts()
{
std::vector <std::string> devices;
std::string path = "/sys/bus/usb/devices/";
std::vector <std::string> files;
DepthSearch( path,
2,
"ttyUSB",
files );
int fileNum = files.size();
for (int i = 0; i < fileNum; i++)
{
// Example "/sys/bus/usb/devices/8-1/8-1:1.1/ttyUSB0"
std::string nodePath = files[i];
int lastSlash = nodePath.find_last_of( "/" );
// This is what we want to return if everything else matches
std::string deviceNode = nodePath.substr( lastSlash + 1 );
// Move down one directory to the interface level
std::string curPath = nodePath.substr( 0, lastSlash );
// Read bInterfaceNumber
int handle = open( (curPath + "/bInterfaceNumber").c_str(),
O_RDONLY );
if (handle == -1)
{
continue;
}
char buff[4];
memset( buff, 0, 4 );
bool bFound = false;
int ret = read( handle, buff, 2 );
if (ret == 2)
{
// Interface 1 or 0
ret = strncmp( buff, "01", 2 );
if (ret == 0)
{
bFound = true;
}
ret = strncmp( buff, "00", 2 );
if (ret == 0)
{
bFound = true;
}
}
close( handle );
if (bFound == false)
{
continue;
}
// Move down one directory to the device level
curPath = curPath.substr( 0, curPath.find_last_of( "/" ) );
// Read idVendor
handle = open( (curPath + "/idVendor").c_str(), O_RDONLY );
if (handle == -1)
{
continue;
}
bFound = false;
ret = read( handle, buff, 4 );
if (ret == 4)
{
ret = strncmp( buff, "05c6", 4 );
if (ret == 0)
{
bFound = true;
}
}
close( handle );
if (bFound == false)
{
continue;
}
// Read idProduct
handle = open( (curPath + "/idProduct").c_str(), O_RDONLY );
if (handle == -1)
{
continue;
}
bFound = false;
ret = read( handle, buff, 4 );
if (ret == 4)
{
ret = strncmp( buff, "920c", 4 );
if (ret == 0)
{
bFound = true;
}
}
close( handle );
if (bFound == false)
{
continue;
}
// Success!
devices.push_back( deviceNode );
}
return devices;
}
T

Answer 1

I know it does not need to be included in case of C, but what about C++?
I think that you should always include the headers you need. I guess your compiler is doing the job for you, if you use the "-Wall" parameter with gcc, you should get a warning.
Under Linux, to know what header you need to include just type man function. Sometime you might get the bash man page, for open you need to indicate the section man 2 read and in the synopsis, you have the required headers. To get those man pages, you also need to install the manpages-dev on Debian based distribution.
To answer to your question, I also had that kind of issue when I was writing C++ programs using a namespace. If you are inside a namespace, try calling this function like that ::read(...)