Here, we will clear all your doubts with examples. Keeping you updated with latest technology trends, Join DataFlair on Telegram. Insertion is done from the back the rear end and deletion is done from the front.
Let us consider a simple scenario to help you get a clear picture of queues.
Learn More about Structures in C Language. Suppose you want to purchase a movie ticket. For that, you need to stand in a queue and wait for your turn, that is, you have to stand at the rear end of the queue. From the above discussion, it is pretty obvious that insertion in a queue takes place from the back and deletion takes place from the front as the first person to enter the queue would be the first to get his job done and leave.
Key takeaway: Both stacks and queues can be static or dynamic according to the way they are implemented. As we already discussed, arrays support the static memory allocation of the data elements of the queue. Therefore, it is important to determine the size of the queue prior to the program run.
Insertion of elements into the queue takes place from the rear end and hence would force the elements to shift forward. Inserting an element into the queue is also called enqueue. Here is a diagrammatic representation of how elements are inserted into a queue:.
In a queue, the deletion of data elements is done from the front.FIFOs in Linux
Deleting the element from the queue is also called dequeue. Similarly, in queues, apart from these 3 main functions, it is necessary to check the overflow and underflow conditions to avoid unfavorable situations. As we already discussed, linked lists support the dynamic memory allocation of the data elements of the queue.
The 3 basic operations of Insertion, Deletion, and Display follow a similar trend as we saw in the array implementation of queues. It is important to note that the condition of queue overflow does not exist in the linked list implementation of queues and the size of the stack is not pre-determined. But, the queue underflow condition still holds true. The role of a circular queue comes into play when we wish to avoid the loss of computer memory using arrays.
It is based on the principle that the rear end of the queue becomes equal to its front end. The circular queue operations are the same as that of a linear queuethat is, insertion, deletion and display and checking of boundary conditions such as overflow and underflow.
The principle FIFO followed by queues gives birth to the various applications of queues. Some of the most popular applications of queues are:. Data Structures are an important concept of every programming language.
Hope, you liked the explanation and can easily implement queues with arrays and linked list. If you have any queries regarding this topic, feel free to let us know your responses in the comment section below! Build your Coding skills with these basic C Programs.First-In, First-Out FIFO is one of the methods commonly used to estimate the value of inventory on hand at the end of an accounting period and the cost of goods sold during the period.
This method assumes that inventory purchased or manufactured first is sold first and newer inventory remains unsold. Thus cost of older inventory is assigned to cost of goods sold and that of newer inventory is assigned to ending inventory. The actual flow of inventory may not exactly match the first-in, first-out pattern.
First-In, First-Out method can be applied in both the periodic inventory system and the perpetual inventory system. The following example illustrates the calculation of ending inventory and cost of goods sold under FIFO method:. Use the following information to calculate the value of inventory on hand on Mar 31 and cost of goods sold during March in FIFO periodic inventory system and under FIFO perpetual inventory system.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I want my program to open a file if it exists, or else create the file.
mkfifo() — Make a FIFO special file
I'm trying the following code but I'm getting a debug assertion at freopen. Would I be better off using fclose and then fopen immediately afterward? If fptr is NULLthen you don't have an open file.
Therefore, you can't freopen it, you should just fopen it. Learn more. Create a file if one doesn't exist - C Ask Question. Asked 8 years ago. Active 3 years, 8 months ago. Viewed k times.
FIFO (First-In-First-Out) approach in Programming
Active Oldest Votes. You typically have to do this in a single syscall, or else you will get a race condition. This will open for reading and writing, creating the file if necessary. Dietrich Epp Dietrich Epp k 29 29 gold badges silver badges bronze badges. It looks like the OP is trying to open it in read-only mode if it already exists I don't understand why they want to create it at all in that case, though. Well, if he doesn't want to write to it, he doesn't need to.
As far as I know, there's no way to open read-only on the condition that it exists without creating a needless race condition. After this section of code I need to read everything from the file, then later write the file from scratch.
Shahbaz Shahbaz This has a race condition, it will fail if another process creates the file between the two calls to fopen.
Making a queue using linked list in C
DietrichEpp Hadn't though of that! Therefore, you can't reopen it. Shahbaz - you're welcome. I think the other answer fails to identify the key point that it will never work. So folks might read that answer and their take away might be about race conditions, especially at it has been upvoted, when it is actually much much simpler.
Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have to use mkfifo in my C program in Ubuntu. But I have an error when I compile: no such file or directory.
But I don't khow how could I do this. You then want to look up the relevant documentation and find the following in man 3 mkfifo :. Learn more. How to make a fifo in C? Ask Question. Asked 4 years, 10 months ago. Active 4 years, 10 months ago. Viewed 2k times. Please include your C program and the command with what you want to compile it. And the full error message, too.
But the profile if you think to your login shell init script isn't written in C, it is in most cases bash. The most probable cause is that the sock directory doesn't exist. Are you sure this directory exists as the sub-directory in which you run your compiled binary? What happens when you use absolute path? Cannot reproduce with gcc 5. Active Oldest Votes. It's because the directory sock doesn't exist. X Tian X Tian 6 6 silver badges 12 12 bronze badges.
Wahoo That it. Is there any way to include all this steps in my code?!? I've shown you how to see what's going on by using cat and echo on different terminals. Now read man 3 mkfifo and read about blocking, permissions etc.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again.
If nothing happens, download the GitHub extension for Visual Studio and try again. Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. C Makefile Shell. Branch: master. Find file. Sign in Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again. Latest commit. Latest commit 2bd Mar 23, However, threads and mutexes alone aren't the only concurrency paradigm available to us.
Very few paradigms map nicely onto heavyweight threads and locking. For example, the Actor model has no explicit locking at all. Let's imagine a classic problem.
We want to write a simple download manager. First, we need to get the data from a high-latency internet connection, then dump that data to a high-latency hard disk. In classic C, waiting for one resource to finish transferring data is time you can't spend on the other one! This is unacceptable since you're dealing with two very slow connections.
When the disk starts spinning up, you don't want your download to slow down! To solve this problem, we introduce a new data structure called a pipe. We create two threads: one for receiving the data from the network, and one for dumping the data to disk. Whenever data is received, it will be pushed into the pipe instead of directly to the disk.
Since the two processes are decoupled by a fast in-memory pipe which is implemented with simple memcpy'swhen one thread lags behind, the other one is free to continue its operation. If the producer is lagging, the consumer will block until there is data.It doesn't need to be too fancy, just a fixed size say chars and can't use any library functions this is for a hobby OS kernel I'm writing, and there's not a lot of functions available for use.
I just tried to make one, then I realized One array and two indecies. One index points to the empty position for the next character to be added. Other index points at the character to be removed when needed. When either getst to the end of the array, reset to beginning. Have you tried googling for Code: queue. It should return more than enough examples. However, there never seems to be anything in the buffer.
It's hanging and not running any code after that. Any ideas? You need to decide when the queue this is the name of this structure is full and empty. The implementation of queue is much more difficult than a stack, especially in c. Have you tried googling for queue. I didn't know :P jk Have you tried googling for Code: queue.
Hmm, googling for a filename. I need to remember that one. OK, I dug up an old thread about doing it with 2 stacks. Hmm, got it now. Dunno what I was thinking using 2 stacks like that :P. Getting Started: Have something to contribute to this discussion? Please be thoughtful, detailed and courteous, and adhere to our posting rules. Edit Preview. H1 H2. Post Reply. Insert Code Block.
Share Post. Permanent Link. Promote Question. Would you like to see this question answered quickly?Sets the access, change, and modification times for the new file. It also sets the change and modification times for the directory that contains the new file.
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The file permission bits in mode are changed by the file creation mask of the process, and then used to set the file permission bits of the FIFO file being created.
If pathname contains a symbolic link, mkfifo fails. For more information on the file creation mask, see umask — Set and retrieve file creation mask ; for information about the file permission bits, see chmod — Change the mode of a file or directory.
If unsuccessful, mkfifo does not create a FIFO file, returns -1, and sets errno to one of the following values: Error Code Description EACCES The process does not have search permission on some component of pathnameor does not have write permission on the parent directory of the file to be created. EEXIST Either the named file refers to a symbolic link, or there is already a file or directory with the given pathname.
Output read 'FIFO's are fun!
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