-->![Using Using](/uploads/1/1/8/9/118946722/436866626.jpg)
For example:
In the filename, if you use a string literal as the argument, you need to remember to use double backslashes rather than a single backslash as you otherwise risk an escape character such as t. Using double backslashes escapes the key, so the string works as it is expected. Your users, of course, do not need to do this! It's just the way quoted strings are handled in C and C++.
Here's a simple example of using fopen:
This code will open test.txt for reading in text mode. To open a file in a binary mode you must add a b to the end of the mode string; for example, 'rb' (for the reading and writing modes, you can add the b either after the plus sign - 'r+b' - or before - 'rb+')
fclose returns zero if the file is closed successfully.
An example of fclose is
To work with text input and output, you use fprintf and fscanf, both of which are similar to their friends printf and scanf except that you must pass the FILE pointer as first argument. For example:
It is also possible to read (or write) a single character at a time--this canbe useful if you wish to perform character-by-character input (for instance,if you need to keep track of every piece of punctuation in a file it wouldmake more sense to read in a single character than to read in a string at atime.) The fgetc function, which takes a file pointer, and returns an int,will let you read a single character from a file:Notice that fgetc returns an int. What this actually means is that when itreads a normal character in the file, it will return a value suitable forstoring in an unsigned char (basically, a number in the range 0 to 255). Onthe other hand, when you're at the very end of the file, you can't get acharacter value--in this case, fgetc will return 'EOF', which is a constant thatindicates that you've reached the end of the file. To see a full exampleusing fgetc in practice, take a look at the example here.
The fputc function allows you to write a character at a time--you might findthis useful if you wanted to copy a file character by character. It lookslike this:Note that the first argument should be in the range of an unsigned char sothat it is a valid character. The second argument is the file to write to.On success, fputc will return the value c, and on failure, it will return EOF.
The declarations for each are similar: Both of these functions deal with blocks of memories - usually arrays. Because they accept pointers, you can also use these functions with other data structures; you can even write structs to a file or a read struct into memory.
Let's look at one function to see how the notation works.
fread takes four arguments. Don't be confused by the declaration of a void *ptr; void means that it is a pointer that can be used for any type variable. The first argument is the name of the array or the address of the structure you want to write to the file. The second argument is the size of each element of the array; it is in bytes. For example, if you have an array of characters, you would want to read it in one byte chunks, so size_of_elements is one. You can use the sizeof operator to get the size of the various datatypes; for example, if you have a variable int x; you can get the size of x with sizeof(x);. This usage works even for structs or arrays. E.g., if you have a variable of a struct type with the name a_struct, you can use sizeof(a_struct) to find out how much memory it is taking up.
e.g.,
The third argument is simply how many elements you want to read or write; for example, if you pass a 100 element array, you want to read no more than 100 elements, so you pass in 100.
The final argument is simply the file pointer we've been using. When fread is used, after being passed an array, fread will read from the file until it has filled the array, and it will return the number of elements actually read. If the file, for example, is only 30 bytes, but you try to read 100 bytes, it will return that it read 30 bytes. To check to ensure the end of file was reached, use the feof function, which accepts a FILE pointer and returns true if the end of the file has been reached.
fwrite is similar in usage, except instead of reading into the memory you write from memory into a file.
For example,
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These packages install run-time components of these libraries: C Runtime (CRT), Standard C, ATL, MFC, C AMP, and OpenMP. For an updated version of these redistributable packages, see KB 3138367. Test your C# code online with.NET Fiddle code editor.
Provides a convenient syntax that ensures the correct use of IDisposable objects. Beginning in C# 8.0, the
using
statement ensures the correct use of IAsyncDisposable objects.In this article, let us discuss how to debug a c program using gdb debugger in 6 simple steps. Write a sample C program with errors for debugging purpose. To learn C program debugging, let us create the following C program that calculates and prints the factorial of a number. However this C program contains some errors in it for our debugging.
Example
The following example shows how to use the
using
statement.Beginning with C# 8.0, you can use the following alternative syntax for the
using
statement that doesn't require braces:Remarks
File and Font are examples of managed types that access unmanaged resources (in this case file handles and device contexts). There are many other kinds of unmanaged resources and class library types that encapsulate them. All such types must implement the IDisposable interface, or the IAsyncDisposable interface.
When the lifetime of an
IDisposable
object is limited to a single method, you should declare and instantiate it in the using
statement. The using
statement calls the Dispose method on the object in the correct way, and (when you use it as shown earlier) it also causes the object itself to go out of scope as soon as Dispose is called. Within the using
block, the object is read-only and can't be modified or reassigned. If the object implements IAsyncDisposable
instead of IDisposable
, the using
statement calls the DisposeAsync and awaits
the returned ValueTask. For more information on IAsyncDisposable, see Implement a DisposeAsync method.The
using
statement ensures that Dispose (or DisposeAsync) is called even if an exception occurs within the using
block. You can achieve the same result by putting the object inside a try
block and then calling Dispose (or DisposeAsync) in a finally
block; in fact, this is how the using
statement is translated by the compiler. The code example earlier expands to the following code at compile time (note the extra curly braces to create the limited scope for the object):The newer
using
statement syntax translates to similar code. The try
block opens where the variable is declared. The finally
block is added at the close of the enclosing block, typically at the end of a method.For more information about the
try
-finally
statement, see the try-finally article.Multiple instances of a type can be declared in a single
using
statement, as shown in the following example. Notice that you can't use implicitly typed variables (var
) when you declare multiple variables in a single statement:![Using Using](/uploads/1/1/8/9/118946722/436866626.jpg)
You can combine multiple declarations of the same type using the new syntax introduced with C# 8 as well, as shown in the following example:
You can instantiate the resource object and then pass the variable to the
using
statement, but this isn't a best practice. In this case, after control leaves the using
block, the object remains in scope but probably has no access to its unmanaged resources. In other words, it's not fully initialized anymore. If you try to use the object outside the using
block, you risk causing an exception to be thrown. For this reason, it's better to instantiate the object in the using
statement and limit its scope to the using
block.For more information about disposing of
IDisposable
objects, see Using objects that implement IDisposable.C# language specification
For more information, see The using statement in the C# Language Specification. The language specification is the definitive source for C# syntax and usage.
See also
In this tutorial, you'll learn how to do file IO, text and binary, in C, using fopen, fwrite, and fread, fprintf, fscanf, fgetc and fputc.
FILE *
For C File I/O you need to use a FILE pointer, which will let the programkeep track of the file being accessed. (You can think of it as the memoryaddress of the file or the location of the file).
For example:
fopen
To open a file you need to use the fopen function, which returns a FILE pointer. Once you've opened a file, you can use the FILE pointer to let the compiler perform input and output functions on the file.In the filename, if you use a string literal as the argument, you need to remember to use double backslashes rather than a single backslash as you otherwise risk an escape character such as t. Using double backslashes escapes the key, so the string works as it is expected. Your users, of course, do not need to do this! It's just the way quoted strings are handled in C and C++.
fopen modes
The allowed modes for fopen are as follows: Note that it's possible for fopen to fail even if your program is perfectly correct: you might try to open a file specified by the user, and that file might not exist (or it might be write-protected). In those cases, fopen will return 0, the NULL pointer.Here's a simple example of using fopen:
This code will open test.txt for reading in text mode. To open a file in a binary mode you must add a b to the end of the mode string; for example, 'rb' (for the reading and writing modes, you can add the b either after the plus sign - 'r+b' - or before - 'rb+')
fclose
When you're done working with a file, you should close it using the functionfclose returns zero if the file is closed successfully.
An example of fclose is
Reading and writing with fprintf, fscanf fputc, and fgetc
![Chopsticks Chopsticks](/uploads/1/1/8/9/118946722/156022256.jpg)
It is also possible to read (or write) a single character at a time--this canbe useful if you wish to perform character-by-character input (for instance,if you need to keep track of every piece of punctuation in a file it wouldmake more sense to read in a single character than to read in a string at atime.) The fgetc function, which takes a file pointer, and returns an int,will let you read a single character from a file:Notice that fgetc returns an int. What this actually means is that when itreads a normal character in the file, it will return a value suitable forstoring in an unsigned char (basically, a number in the range 0 to 255). Onthe other hand, when you're at the very end of the file, you can't get acharacter value--in this case, fgetc will return 'EOF', which is a constant thatindicates that you've reached the end of the file. To see a full exampleusing fgetc in practice, take a look at the example here.
The fputc function allows you to write a character at a time--you might findthis useful if you wanted to copy a file character by character. It lookslike this:Note that the first argument should be in the range of an unsigned char sothat it is a valid character. The second argument is the file to write to.On success, fputc will return the value c, and on failure, it will return EOF.
Binary file I/O - fread and fwrite
For binary File I/O you use fread and fwrite.Using Cscope
The declarations for each are similar: Both of these functions deal with blocks of memories - usually arrays. Because they accept pointers, you can also use these functions with other data structures; you can even write structs to a file or a read struct into memory.
Using C#
Let's look at one function to see how the notation works.
fread takes four arguments. Don't be confused by the declaration of a void *ptr; void means that it is a pointer that can be used for any type variable. The first argument is the name of the array or the address of the structure you want to write to the file. The second argument is the size of each element of the array; it is in bytes. For example, if you have an array of characters, you would want to read it in one byte chunks, so size_of_elements is one. You can use the sizeof operator to get the size of the various datatypes; for example, if you have a variable int x; you can get the size of x with sizeof(x);. This usage works even for structs or arrays. E.g., if you have a variable of a struct type with the name a_struct, you can use sizeof(a_struct) to find out how much memory it is taking up.
Using Crimp Beads
e.g.,
The third argument is simply how many elements you want to read or write; for example, if you pass a 100 element array, you want to read no more than 100 elements, so you pass in 100.
The final argument is simply the file pointer we've been using. When fread is used, after being passed an array, fread will read from the file until it has filled the array, and it will return the number of elements actually read. If the file, for example, is only 30 bytes, but you try to read 100 bytes, it will return that it read 30 bytes. To check to ensure the end of file was reached, use the feof function, which accepts a FILE pointer and returns true if the end of the file has been reached.
Using Countif In Excel
fwrite is similar in usage, except instead of reading into the memory you write from memory into a file.
For example,
Quiz yourself
Previous: Strings
Next: Typecasting
Back to C Tutorial Index
Related articles
More on working with files in C
C++ file IO
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