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  1. Friedrich-Alexander-Universität
  2. Technische Fakultät
  3. Department Informatik
Friedrich-Alexander-Universität Lehrstuhl für Informatik 4 (Systemsoftware)
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  • Systemnahe Programmierung in C (für Wiederholer)
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          • Linux libc-Doku
            • Intern

            Linux libc-Doku

            Files | Functions
            Input/Output

            Files

            file  stdio.h
             

            Functions

            int printf (const char *format,...)
             Print formatted data to stdout More...
             
            int fprintf (FILE *stream, const char *format,...)
             Print formatted data to stream. More...
             
            int fgetc (FILE *stream)
             Read a character. More...
             
            char * fgets (char *s, int size, FILE *stream)
             Read a string. More...
             
            int fputc (int c, FILE *stream)
             Write a character. More...
             
            int fputs (const char *s, FILE *stream)
             Write a string. More...
             
            void perror (const char *s)
             Print an error message. More...
             
            int feof (FILE *stream)
             Test end-of-file indicator of a file stream. More...
             
            int ferror (FILE *stream)
             Test error indicator of a file stream. More...
             

            Detailed Description

            This code snippet illustrates the usage of fgetc() and fputc():

            int c;
            while ((c = fgetc(stdin)) != EOF) {
            if (fputc((unsigned char) c, stdout) == EOF) {
            perror("fputc");
            exit(EXIT_FAILURE);
            }
            }
            if (ferror(stdin)) {
            // error
            }
            // no error; end of file reached
            ferror
            int ferror(FILE *stream)
            Test error indicator of a file stream.
            fgetc
            int fgetc(FILE *stream)
            Read a character.
            perror
            void perror(const char *s)
            Print an error message.
            fputc
            int fputc(int c, FILE *stream)
            Write a character.
            exit
            void exit(int status)
            Terminate process.

            This code snippet illustrates the usage of fgets() and fputs():

            char buffer[1024];
            char *check;
            // reads at most 1023 characters per iteration
            while ((check = fgets(buffer, 1024, stdin)) != NULL) {
            if (fputs(buffer, stdout) == EOF) {
            perror("fputs");
            exit(EXIT_FAILURE);
            }
            }
            if (ferror(stdin)) {
            // error
            }
            // alternative to ferror():
            // if (feof(stdin)) {
            // // no error; end of file reached
            // } else {
            // // error
            // }
            fgets
            char * fgets(char *s, int size, FILE *stream)
            Read a string.
            fputs
            int fputs(const char *s, FILE *stream)
            Write a string.

            Function Documentation

            int printf ( const char *  format,
              ... 
            )

            The printf() (print formatted) function produces output according to a format string as specified in format and writes it stdout. The format string defines the structure of the output (i.e., how many and which additional arguments) and the additional parameter of the printf() function are used to replace the arguments in the format string with actual data. It is important that the number of additional parameter matches the number of arguments of the format string.

            An argument in the format string starts with a %. The following table shows some important arguments, however, there are several more options described in the manpage of printf() (man 3 printf):

            Type Description
            i, d integer
            u unsigned integer
            f floating point
            p pointer
            s string
            c character

            Example:

            int i = 5;
            char c = 'a';
            void *p = &i;
            printf("Hello World!\n"); // no arguments
            printf("$> i: %i\n$> c: %c\n$> f: %f\n \
            $> p: %p\n", i, c, 3.14, p); // including arguments
            printf
            int printf(const char *format,...)
            Print formatted data to stdout
            // produces:
            Hello world!
            $> i: 5
            $> c: a
            $> f: 3.140000
            $> p: 0x7ffebe5dbe34

            We do not expect error handling for printf().

            Parameters
            formatformat string
            ...arguments
            Return values
            >=0number of characters printed
            <0on error, errno is set
            int fprintf ( FILE *  stream,
            const char *  format,
              ... 
            )

            The fprintf() (file stream print formatted) function is very similar to printf(), except that it does not write to stdout, but to stream.

            For more details see printf().

            // both lines write to stdout
            fprintf(stdout, "Hello world!\n");
            printf("Hello world!\n");
            // write to stderr
            fprintf(stderr, "Error in file '%s' at line %u\n", __FILE__, __LINE__);
            fprintf
            int fprintf(FILE *stream, const char *format,...)
            Print formatted data to stream.

            We do not expect error handling for fprintf().

            Parameters
            streamfile stream to write
            formatformat string, see printf()
            ...arguments
            Return values
            >=0number of characters printed
            <0on error, errno is set
            int fgetc ( FILE *  stream)

            The fgetc() (file stream get character) function returns an unsigned char casted to an int read from a stream or returns EOF.

            fgetc() returns EOF on error or when the end of the file is reached. To distinguish these two events the feof() or ferror() function can be used. Be aware, that the return value of fgetc() must be saved in an int (and not in an unsigned char) in order to distinguish EOF and 0xFF (which is the character ÿ when interpreted as ISO-8859-1).

            Parameters
            streamfile stream to read
            Return values
            EOFon error or end of file, errno is set on error
            !=EOFunsigned char read from stream
            char* fgets ( char *  s,
            int  size,
            FILE *  stream 
            )

            The fgets() (file stream get string) function reads at most size-1 characters from stream and saves them in the buffer pointed to by s. It terminates the string in s with a null byte (\0).

            fgets() reads in characters until it finds a newline character (\n) or it has read size-1 characters. If an error occurred or the end of file was reached it returns NULL. The ferror() and feof() functions can be used to distinguish these two events.

            Parameters
            sbuffer to write to
            sizesize of the buffer
            streamfile stream to read
            Return values
            NULLon error or end of file, errno is set on error
            !=NULLpointer to s
            int fputc ( int  c,
            FILE *  stream 
            )

            The fputc() (file stream put character) function writes the character c to stream.

            We do not expect error handling when using fputc().

            Parameters
            cchar to print (casted to an int)
            streamfile stream to write
            Return values
            !=EOFprinted char
            EOFon error, errno is set
            int fputs ( const char *  s,
            FILE *  stream 
            )

            The fputs() (file stream put string) function writes the string pointed to by s to stream.

            We do not expect error handling when using fputs().

            Parameters
            sstring to be printed
            streamfile stream to write
            Return values
            >=0on success
            EOFon error, errno is set
            void perror ( const char *  s)

            The perror() (print error) function produces an error message on stderr printing the string in s followed by a human-readable description of the value in errno. This is especially helpful after a failed call to a system or library function, which sets the errno variable (e.g., malloc()).

            Parameters
            sstring printed before the actual error message
            int feof ( FILE *  stream)

            The feof() (file stream end of file) function tests the EOF indicator of stream.

            Parameters
            streamfile stream to test
            Return values
            0end-of-file indicator is not set
            !=0end-of-file indicator is set
            int ferror ( FILE *  stream)

            The ferror() (file stream error) function tests the error indicator of stream.

            Parameters
            streamfile stream to test
            Return values
            0error indicator is not set
            !=0error indicator is set
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