C/C++ f 系列

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C/C++ f 系列

fopen

fgetc

  • #include <stdio.h>
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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);
  • fgetc()
    • get a byte from a stream
    • 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 a null byte (aq\0aq).
    • 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 terminating null byte (aq\0aq) 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.

      param

  • fgets
    • str – 這是字符串讀取存儲的字符數組的指針。
    • n – 這是最大的被讀取的字符數（包括最後的空字符）。通常情況下，通過使用str是數組的長度。
    • stream – 這是一個文件對象標識流中讀取字符的指針。

      return

  • fgetc(), getc() and getchar()
    • 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
    • NULL on error or when end of file occurs while no characters have been read.
  • ungetc()
    • c on success, or EOF on error.

e.g.

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#include <stdio.h>

int main()
{
   FILE *fp;
   char str[60];

   /* opening file for reading */
   fp = fopen("file.txt" , "r");
   if(fp == NULL) {
      perror("Error opening file");
      return(-1);
   }
   if( fgets (str, 60, fp)!=NULL ) {
      /* writing content to stdout */
      puts(str);
   }
   fclose(fp);
   
   return(0);
}

reference

clearerr, feof, ferror, fileno

  • #include <stdio.h>
  • check and reset stream status
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    void clearerr(FILE *stream);
    int feof(FILE *stream);
    int ferror(FILE *stream);
    int fileno(FILE *stream);
  • clearerr()
    • clears the end-of-file and error indicators for the stream pointed to by stream.
  • 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().
  • 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.
  • fileno()
    • examines the argument stream and returns its integer descriptor.

param

  • stream – 這是一個文件 FILE 對象的標識流的指針。

    return

  • feof
    • 這個函數返回一個非零值時，與該流關聯的文件結束指示器設置
    • 否則返回零。

e.g.

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#include <stdio.h>

int main ()
{
   FILE *fp;
   int c;
   int n = 0;
  
   fp = fopen("file.txt","r");
   if(fp == NULL) 
   {
      perror("Error in opening file");
      return(-1);
   }
   while(!feof(fp))
   {
      c = fgetc(fp);
      printf("%c", c);
   }
  
   fclose(fp);
   
   return(0);
}

reference

  • feof() - C庫函數 - C語言標準庫
  • feof(3): check/reset stream status - Linux man page

    fclose

    • #include <stdio.h>
  • flushes the stream pointed to by stream (writing any buffered output data using fflush(3))
  • closes the underlying file descriptor.

    return

  • Upon successful completion, 0 is returned.
  • Otherwise, EOF is returned and errno is set to indicate the error.
    • In either case, any further access (including another call to fclose()) to the stream results in undefined behavior.

reference