Read Text File into String (with StreamReader) Let's look under the hood of the previous example. Method File.ReadAllText is implemented similarly to the following code. The using statement ensures that method StreamReader.Dispose is called. Example: Synchronous read in a console app. The following example shows a synchronous read operation within a console app. This example opens the text file using a stream reader, copies the contents to a string, and outputs the string to the console. The null coalescing operator (called the Logical Defined-Or operator in Perl) is a binary operator that is part of the syntax for a basic conditional expression in several programming languages, including C#, PowerShell as of version 7.0.0, Perl as of version 5.10, Swift, and PHP 7.0.0. C programming language also allows to define various other types of variables, which we will cover in subsequent chapters like Enumeration, Pointer, Array, Structure, Union, etc. For this chapter, let us study only basic variable types. The File.ReadAllText method calls into other methods in the.NET Framework. At some point, low-level functions in Windows read in all the text using buffered reads. The text data is then put into an object with string character data. Result: The File.ReadAllText.
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Data types in c refer to an extensive system used for declaring variables or functions of different types. The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted.
The types in C can be classified as follows −
| Sr.No. | Types & Description |
|---|---|
| 1 | Basic Types They are arithmetic types and are further classified into: (a) integer types and (b) floating-point types. |
| 2 | Enumerated types They are again arithmetic types and they are used to define variables that can only assign certain discrete integer values throughout the program. |
| 3 | The type void The type specifier void indicates that no value is available. |
| 4 | Derived types They include (a) Pointer types, (b) Array types, (c) Structure types, (d) Union types and (e) Function types. |
The array types and structure types are referred collectively as the aggregate types. The type of a function specifies the type of the function's return value. We will see the basic types in the following section, where as other types will be covered in the upcoming chapters.
Integer Types
The following table provides the details of standard integer types with their storage sizes and value ranges −
| Type | Storage size | Value range |
|---|---|---|
| char | 1 byte | -128 to 127 or 0 to 255 |
| unsigned char | 1 byte | 0 to 255 |
| signed char | 1 byte | -128 to 127 |
| int | 2 or 4 bytes | -32,768 to 32,767 or -2,147,483,648 to 2,147,483,647 |
| unsigned int | 2 or 4 bytes | 0 to 65,535 or 0 to 4,294,967,295 |
| short | 2 bytes | -32,768 to 32,767 |
| unsigned short | 2 bytes | 0 to 65,535 |
| long | 8 bytes or (4bytes for 32 bit OS) | -9223372036854775808 to 9223372036854775807 |
| unsigned long | 8 bytes | 0 to 18446744073709551615 |
To get the exact size of a type or a variable on a particular platform, you can use the sizeof operator. The expressions sizeof(type) yields the storage size of the object or type in bytes. Given below is an example to get the size of various type on a machine using different constant defined in limits.h header file −
When you compile and execute the above program, it produces the following result on Linux −
Floating-Point Types
The following table provide the details of standard floating-point types with storage sizes and value ranges and their precision −
| Type | Storage size | Value range | Precision |
|---|---|---|---|
| float | 4 byte | 1.2E-38 to 3.4E+38 | 6 decimal places |
| double | 8 byte | 2.3E-308 to 1.7E+308 | 15 decimal places |
| long double | 10 byte | 3.4E-4932 to 1.1E+4932 | 19 decimal places |
The header file float.h defines macros that allow you to use these values and other details about the binary representation of real numbers in your programs. The following example prints the storage space taken by a float type and its range values −
When you compile and execute the above program, it produces the following result on Linux −
The void Type
The void type specifies that no value is available. It is used in three kinds of situations −
| Sr.No. | Types & Description |
|---|---|
| 1 | Function returns as void There are various functions in C which do not return any value or you can say they return void. A function with no return value has the return type as void. For example, void exit (int status); |
| 2 | Function arguments as void There are various functions in C which do not accept any parameter. A function with no parameter can accept a void. For example, int rand(void); |
| 3 | Pointers to void A pointer of type void * represents the address of an object, but not its type. For example, a memory allocation function void *malloc( size_t size ); returns a pointer to void which can be casted to any data type. |
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When we say Input, it means to feed some data into a program. An input can be given in the form of a file or from the command line. C programming provides a set of built-in functions to read the given input and feed it to the program as per requirement.
When we say Output, it means to display some data on screen, printer, or in any file. C programming provides a set of built-in functions to output the data on the computer screen as well as to save it in text or binary files.
The Standard Files
C programming treats all the devices as files. So devices such as the display are addressed in the same way as files and the following three files are automatically opened when a program executes to provide access to the keyboard and screen.
| Standard File | File Pointer | Device |
|---|---|---|
| Standard input | stdin | Keyboard |
| Standard output | stdout | Screen |
| Standard error | stderr | Your screen |
C# Read All Lines From Text File
The file pointers are the means to access the file for reading and writing purpose. This section explains how to read values from the screen and how to print the result on the screen.
The getchar() and putchar() Functions
The int getchar(void) function reads the next available character from the screen and returns it as an integer. This function reads only single character at a time. You can use this method in the loop in case you want to read more than one character from the screen.
The int putchar(int c) function puts the passed character on the screen and returns the same character. This function puts only single character at a time. You can use this method in the loop in case you want to display more than one character on the screen. Check the following example −
When the above code is compiled and executed, it waits for you to input some text. When you enter a text and press enter, then the program proceeds and reads only a single character and displays it as follows −
The gets() and puts() Functions
The char *gets(char *s) function reads a line from stdin into the buffer pointed to by s until either a terminating newline or EOF (End of File).
The int puts(const char *s) function writes the string 's' and 'a' trailing newline to stdout.
NOTE: Though it has been deprecated to use gets() function, Instead of using gets, you want to use fgets().
When the above code is compiled and executed, it waits for you to input some text. When you enter a text and press enter, then the program proceeds and reads the complete line till end, and displays it as follows −
The scanf() and printf() Functions
C# Read All Text From File To String
The int scanf(const char *format, ...) function reads the input from the standard input stream stdin and scans that input according to the format provided.
The int printf(const char *format, ...) function writes the output to the standard output stream stdout and produces the output according to the format provided.
C# Read All Text From File
The format can be a simple constant string, but you can specify %s, %d, %c, %f, etc., to print or read strings, integer, character or float respectively. There are many other formatting options available which can be used based on requirements. Let us now proceed with a simple example to understand the concepts better −
When the above code is compiled and executed, it waits for you to input some text. When you enter a text and press enter, then program proceeds and reads the input and displays it as follows −
Here, it should be noted that scanf() expects input in the same format as you provided %s and %d, which means you have to provide valid inputs like 'string integer'. If you provide 'string string' or 'integer integer', then it will be assumed as wrong input. Secondly, while reading a string, scanf() stops reading as soon as it encounters a space, so 'this is test' are three strings for scanf().