Linux Programming

Vaclav_ wrote:

I have quit checking the actual file descriptor because perror gives a more information when it fails.

	// allocate socket
	socket_fd = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
#ifdef TRACE
	cout << "Socket errno " << dec << errno << "  @line " << __LINE__ << endl;
	perror("STATUS allocate socket ");

this call sets the errno to 22 -  AFTER perror is executed with errno being set to 0 success!  
	
cout << "socket_fd  " << dec << socket_fd << endl;

this call 
	cout << "Socket errno " << dec << errno << "  @line " << __LINE__ << endl;
    //exit(-1);
#endif


	// reallocate socket
here the errno is still set to 22 ! 

	socket_fd = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
#ifdef TRACE
	cout << "Socket errno " << dec << errno << "  @line " << __LINE__ << endl;
	perror("STATUS allocate socket ");
	cout << "socket_fd  " << dec << socket_fd << endl;
	cout << "Socket errno " << dec << errno << "  @line " << __LINE__ << endl;
    exit(-1);
#endif

SERVER_X86_228 
RPI_ARM  
date version Feb 29 2020
test time 13:37:53
STATUS allocate socket : Success
 BREAK @line 47
Socket errno 0  @line 61
socket_fd  3
Socket errno 22  @line 64
Socket errno 22  @line 72
socket_fd  4
Socket errno 22  @line 75
STATUS allocate socket : Invalid argument

When a system call fails, it usually returns -1 and sets the variable
       errno to a value describing what went wrong.  (These values can be
       found in <errno.h>.)  Many library functions do likewise.  The
       function perror() serves to translate this error code into human-
       readable form.  Note that errno is undefined after a successful
       system call or library function call: this call may well change this
       variable, even though it succeeds, for example because it internally
       used some other library function that failed.  Thus, if a failing
       call is not immediately followed by a call to perror(), the value of
       errno should be saved.

	errcode = getaddrinfo("z_desktop", NULL, &hints, &res);
	//perror("STATE getaddrinfo");
	if (errcode != 0) {           // call returns "-errors " 
		//cout <<"errno " << dec << errno << endl;
		perror("STATE getaddrinfo");     
// perror prints "Success" !  getaddrinfo does not sets errno ! 
		//cout << " errcode (?) " << dec << errcode << endl;
		//cout << "hints.ai_addr " << dec <<  hints.ai_addr << endl;
		//cout <<"hints.ai_family  " << hints.ai_family << endl;
		return -1;
	}

cmd /k yourapp

Richard MacCutchan wrote:

*I think -n will process the makefile but not execute the resulting statements
Possibly -p to list everything

make -p > make.out 2>&1

$ make -p hello.c | wc -l
1481
$

$ make -p hello > make.out 2>&1
$ head -20 make.out
cc     hello.c   -o hello
# GNU Make 4.2.1
# Built for arm-unknown-linux-gnueabihf
# Copyright (C) 1988-2016 Free Software Foundation, Inc.
# License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
# This is free software: you are free to change and redistribute it.
# There is NO WARRANTY, to the extent permitted by law.

# Make data base, printed on Tue Feb  4 12:02:00 2020

# Variables

# automatic
<D = $(patsubst %/,%,$(dir $<))
# automatic
?F = $(notdir $?)
# default
.SHELLFLAGS := -c
# environment
XDG_SESSION_CLASS = user
$