Shulou(Shulou.com)06/03 Report--

one。 Error reporting the 1.perror () function is a simple and uniform way to report errors. Many functions in the ansi c function library call the operating system to accomplish certain tasks, especially the Icano function. At any time, when the operating system executes something as required, there is the possibility of failure. The standard library function passes this information to the user program after saving the error code in an external integer variable errno (defined in errno.h), indicating the exact reason for the failure of the operation.

The prototype of the 2.perror () function:

# include

Void perror (charconst * message)

If message is not NULL and points to a non-empty string, the perror function prints out the string, followed by a semicolon and a space, and then prints out a message explaining the current error code of errno.

The biggest advantage of the 3.perrno function is that it is easy to use. Good programming practice requires that any read of an operation that may cause an error should be checked after execution to determine whether it was executed successfully.

Description:

Errno is set only if a library function fails. When the function executes successfully, the value of errno does not need to be changed. Therefore, it is not possible to determine whether an error has occurred by testing the value of errno. So it only makes sense to check the value of errno when the called function indicates that an error has occurred.

two。 Terminate execution 1. The function that terminates execution is exit, which is used to terminate the execution of a program.

two。 Its prototype is:

# include

Void exit (intstatus)

The 3.status parameter is returned to the operating system to indicate whether the program has completed properly.

This value is the same as the integer state value returned by the main () function. The predefined symbols EXIT_SUCCESS and EXIT__FAILURE indicate whether the termination of the program succeeds or fails, respectively.

4. You can use this function when the program finds an error condition that makes it impossible to continue execution. We often call the exit termination program after we call perrno.

5. The function does not return a value. When the exit function ends, the program has disappeared.

three。 Text stream 1. There are two types of streams, text (text) streams and binary (binary) streams.

two。 Some features of text flow may vary from system to system. One of these is the maximum length of the line of the text. The standard stipulates that at least 254 characters are allowed. Another feature that may be different is the way lines of text end.

1 > in MS-DOS systems, text lines are scheduled to end with a carriage return and a newline character.

2 > only a newline character is used at the end of the UNIX system.

3. Standard lines of text are defined as zero or more characters, followed by a newline character that indicates the end.

four。 Binary stream 1. Bytes in a binary stream are written to a file or device exactly as they are written by the program, and read into the program exactly as they are read from the file or device.

two。 This type of stream is suitable for non-text data, but it can also be used in a text file if the Istroke O function modifies the end-of-line character of a text file.

One of the declarations contained in the fifth file 1.stdio.h is the FILE structure. FILE is a data structure for accessing a stream.

two。 If several streams are activated at the same time, each stream has a corresponding FILE associated with it. In order to perform some operations on the flow, you can call some appropriate functions and pass them a FILE parameter associated with the flow.

3. For each ANSI C program, the runtime system must provide at least three streams:

1 > standard input: standard input is the source of input by default.

2 > standard output: standard output is the default output setting

3 > standard error: this is where the error is written. The Perror function also writes its output to this place. In many systems, standard output and standard error are the same by default. However, preparing a different stream for the error message means that even if the standard output is redirected elsewhere, the error message will still appear on the screen or other default output device.

The names of these streams are stdin, stout, and stderr. They are all pointers to FILE structures.

4. Many operating systems allow users to modify default standard input and output devices during program execution.

For example:

Both MS-DOS and UNIX systems support input / output redirection using the following methods: program

Answer

When the program executes, it will read as standard input from the file data instead of the keyboard, and it will write the standard output to the file answer instead of to the screen.

5. The program declares a pointer variable of type FILE * for each file that must be active at the same time. This pointer points to the FILE structure, which is used by the stream when it is active.

6. The stream is opened by calling the fopen function. To open a stream, you must specify the files or devices that need to be accessed and how they are accessed (for example, read, write, or both read and write). Fopen () and the operating system verify that the file or device does exist and initialize the FILE structure. Then, read or write to the file as needed. Finally, the flose function is called to close the stream. Closing a stream prevents the files associated with it from being accessed again, ensures that any data stored in the buffer is correctly written to the file, and frees the FILE structure so that it can be used in other files.

The 7.I/O function processes data in three basic forms: single characters, lines of text, and binary data. For each form, there is a specific set of functions that deal with them.

8. Open stream

The 1 > fopen () function opens a specific file and associates a stream with the file. The prototype is as follows:

FILE * fopen (char const * name,char const * mode)

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