In this hyper-connected electronic world, knowing how to send and receive data remotely with sockets is crucial. In this article, we will see how a socket is essentially a digital “plug” that we can attach to a local or remote address in order to establish a connection. We will also explore the architecture and system calls that allow us to create not only a client but also a server...
Anyone who’s ever been confronted to segfaults and bus error will already be familiar with the idea of signals. We get a SIGSEGV or a SIGBUS which ends our program’s execution without notice, without explanation and without appeal. But what really is a signal? Is it more than just the operating system’s police baton? And how can we send, block and even intercept one within our...
For efficiency or by necessity, a program can be concurrent rather than sequential. Thanks to its concurrent programming and with its child processes or threads and mutexes, it will be able to perform multiple tasks simultaneously. In a previous article, we came to understand how to create child processes, which are one way to implement concurrent programming. Here, we will concentrate on threads...
Underlying any software development is program error detection and analysis. But then an external library function or system call fails, how can we understand what went wrong? These functions usually return -1 or NULL, but they also store the reason behind their failure in errno. Let’s see what errno actually is, and how to retrieve, interpret and print it out. What is Errno? Errno...
By default, it is difficult to get two processes to communicate with each other. As we’ve seen in a previous article, even parent and child processes don’t share the same memory space. So we need to find ways to establish inter-process communication. One of these communication mechanisms is the pipe. What is a Pipe? A pipe is a section of shared memory meant to facilitate the...
The available system calls to create or open, read, write, and delete a file in C all make use of a file descriptor. So let’s discover how the operating system handles references to open files and how to manipulate files in our programs. What is a File Descriptor? In Unix type systems, a file descriptor (fd for short) is a small positive integer used as reference to an open file in a...
In order to execute another program within ours or to execute part of our program simultaneously, it can often be very useful to create child processes. Then, all we need to do is patiently wait for them to finish their tasks, or, if we’re feeling particularly murderous, kill them prematurely! So what exactly is a process? How can we create child processes, and why wait for them or kill...
A variable is a name we give to a memory storage area that our program can then manipulate. We can specify its size and its type depending on the values it will contain (char, int, long). But we can also control its lifespan and its scope when we declare it. This is why we need to be able to distinguish between local, global and static variables when we program in C. Local Variables Local...
Computers only know one language: binary. Our many programming languages allow us to give instructions in a human-readable format, which are then translated into long sequences of 0s and 1s. Although this level of abstraction is essential to us humans, it can be useful and even much more efficient to manipulate bits directly, thanks to bit shifting and bitwise operations. We previously had the...
In compiled programming languages like C, it is often useful, or even necessary, to allocate memory dynamically on the heap, in order to accommodate variables of larger or uncertain size. The malloc function allows us to ask the operating system to allocate an area of memory to be used in our program. In order to use malloc effectively, we must understand how two different parts of memory...