用标准IO将标准输入复制到标准输出

预备知识：

1.NAME

       fgetc,  fgets,  getc,  getchar,  gets, ungetc - input of characters and

       strings

SYNOPSIS

       #include

       int fgetc(FILE *stream);

       char *fgets(char *s, int size, FILE *stream);

       int getc(FILE *stream);

       int getchar(void);

       char *gets(char *s);

       int ungetc(int c, FILE *stream);

DESCRIPTION

       fgetc() reads the next character from  stream  and  returns  it  as  an

       unsigned char cast to an int, or EOF on end of file or error.

       getc()  is equivalent to fgetc() except that it may be implemented as a

       macro which evaluates stream more than once.

       getchar() is equivalent to getc(stdin).

       gets() reads a line from stdin into the buffer pointed to  by  s  until

       either  a  terminating newline or EOF, which it replaces with '\0'.  No

       check for buffer overrun is performed (see BUGS below).

       fgets() reads in at most one less than size characters from stream  and

       stores  them  into  the buffer pointed to by s.  Reading stops after an

       EOF or a newline.  If a newline is read, it is stored into the  buffer.

       A '\0' is stored after the last character in the buffer.

       ungetc()  pushes  c  back to stream, cast to unsigned char, where it is

       available for subsequent read operations.  Pushed-back characters  will

       be returned in reverse order; only one pushback is guaranteed.

RETURN VALUE

       fgetc(),  getc() and getchar() return the character read as an unsigned

       char cast to an int or EOF on end of file or error.

       gets() and fgets() return s on success, and NULL on error or  when  end

       of file occurs while no characters have been read.

       ungetc() returns c on success, or EOF on error.

2.NAME

       fputc, fputs, putc, putchar, puts - output of characters and strings

SYNOPSIS

       #include

       int fputc(int c, FILE *stream);

       int fputs(const char *s, FILE *stream);

       int putc(int c, FILE *stream);

       int putchar(int c);

       int puts(const char *s);

DESCRIPTION

       fputc() writes the character c, cast to an unsigned char, to stream.

       fputs() writes the string s to stream, without its trailing '\0'.

       putc()  is equivalent to fputc() except that it may be implemented as a

       macro which evaluates stream more than once.

       putchar(c); is equivalent to putc(c,stdout).

       puts() writes the string s and a trailing newline to stdout.

RETURN VALUE

       fputc(), putc() and  putchar()  return  the  character  written  as  an

       unsigned char cast to an int or EOF on error.

       puts()  and  fputs()  return a nonnegative number on success, or EOF on

       error.

3.NAME

       clearerr, feof, ferror, fileno - check and reset stream status

SYNOPSIS

       #include

       void clearerr(FILE *stream);

       int feof(FILE *stream);

       int ferror(FILE *stream);

       int fileno(FILE *stream);

DESCRIPTION

       The function clearerr() clears the end-of-file and error indicators for

       the stream pointed to by stream.

       The function feof() tests the  end-of-file  indicator  for  the  stream

       pointed  to by stream, returning nonzero if it is set.  The end-of-file

       indicator can only be cleared by the function clearerr().

       The function ferror() tests the error indicator for the stream  pointed

       to  by stream, returning nonzero if it is set.  The error indicator can

       only be reset by the clearerr() function.

       The function fileno() examines the  argument  stream  and  returns  its

       integer descriptor.

本程序用标准IO将标准输入复制到标准输出（能复制任一UNIX普通文件）。

程序清单：

#include <stdio.h> //printf(),getc(),putc(),ferror(),EOF

#include <stdlib.h> //exit(0),exit(1);


int main(int argc,char * argv[])
{
    char c;
    while((c = getc(stdin))!=EOF)
    {
        if(putc(c,stdout) == EOF)
        {
            printf("output error!\n");
            exit(1);
        }
        if(ferror(stdin))
        {
            printf("input error\n");
            exit(1);
        }
    }
    exit(0);
}

编译源文件：

  gcc -o stdinout stdinout.c

执行程序：

./stdinout

Hello

Hello

How old are you?

How old are you?

你怎么老是复制我呀？

你怎么老是复制我呀？

若以以下方式执行该程序：

./stdinout < infile > outfile

那么名为infile文件的内容复制到名为outfile的文件中。