标准c的io操作

1. io操作实例

2. io函数分析

<1>. io 操作实例 

1.1  文本文件读取

#include <stdio.h> // file io operators

#include <stdlib.h>

int main(int argc, char* argv[])

{

FILE* fp;

int ch;

long int count = 0;

if (argc != 2)

{

printf("usage : %s filename", argv[0]);

return EXIT_SUCCESS;

}

// open file

if ( (fp = fopen(argv[1], "r")) == NULL )

{

printf("can not open the file\n");

return EXIT_FAILURE;

}

while ( (ch = getc(fp)) != EOF )

{

printf("%c", ch);

count++;

}

// close file

fclose(fp);

// print how many chars in the file

printf("the file has %ld chars\n", count);

return EXIT_SUCCESS;

}

1.2 二进制文件读取

/*

 * file_op.c

 *

 *  Created on: Apr 19, 2011

 *      Author: xuqiang

 */

#include <stdio.h>

#include <stdlib.h>

#include "file_op.h"

void randbin()

{

const int NUMBER_SIZE = 1000;

double numbers[NUMBER_SIZE];

double read_numbers[NUMBER_SIZE];

const char* file = "number.dat";

long pos;

FILE* fp;

int index;

double value;

// make a random array

int i;

for (i = 0; i < NUMBER_SIZE; ++i)

{

numbers[i] = i;

}

// open file

if ( (fp =  fopen(file, "wb")) == NULL )

{

printf("error to open the file for writing\n");

exit(1);

}

// write the data to file

fwrite(numbers, sizeof(double), NUMBER_SIZE,fp);

fclose(fp);

// open the file for read

if ( (fp = fopen(file, "rb")) == NULL )

{

printf("error open the file for read\n");

exit(1);

}

printf("enter a index from 0 to %d :", NUMBER_SIZE - 1);

scanf("%d", &index);

pos = index * sizeof(double);

fseek(fp, pos, SEEK_SET);

fread(&value, sizeof(double), 1, fp);

printf("the number is %f\n", value);

fclose(fp);

printf("done\n");

exit(0);

}

<2>. io 函数分析 

下面是在我的ubuntu上的<stdio.h>文件比较重要函数:

/* End of file character. 定义文件结尾

   Some things throughout the library rely on this being -1.  */

#ifndef EOF

# define EOF (-1)

#endif 

/* The possibilities for the third argument to `fseek'. 定义在fseek函数中使用的产量

   These values should not be changed.  */

#define SEEK_SET 0 /* Seek from beginning of file.文件开始  */

#define SEEK_CUR 1 /* Seek from current position.当前文件指针位置  */

#define SEEK_END 2 /* Seek from end of file. 文件结尾 */

 /* Rename file OLD to NEW. 重命名文件 */

extern int rename (__const char *__old, __const char *__new) __THROW;

/* Close STREAM.

关闭文件流

   This function is a possible cancellation point and therefore not

   marked with __THROW.  */

extern int fclose (FILE *__stream); 

/* Flush STREAM, or all streams if STREAM is NULL.

刷新缓冲区，如果参数为null的话，将刷新所有的缓冲区

   This function is a possible cancellation point and therefore not

   marked with __THROW.  */

extern int fflush (FILE *__stream); 

/* 打开文件，__filename带打开的文件名， __modes打开方式，例如读写*/ 

extern FILE *fopen (__const char *__restrict __filename,

   __const char *__restrict __modes) __wur; 

/* If BUF is NULL, make STREAM unbuffered.更改标准io的缓存方式

   Else make it use buffer BUF, of size BUFSIZ.  */

extern void setbuf (FILE *__restrict __stream, char *__restrict __buf) __THROW; 

 /* If BUF is NULL, make STREAM unbuffered.

   Else make it use SIZE bytes of BUF for buffering.  */

extern void setbuffer (FILE *__restrict __stream, char *__restrict __buf,

      size_t __size) __THROW;

/* Make STREAM line-buffered. 设置成行缓存方式 */

extern void setlinebuf (FILE *__stream) __THROW;

/* Write formatted output to S. 一个比较常用的函数，格式化一个字符串，类似于c#中的String.Format */

extern int sprintf (char *__restrict __s,

   __const char *__restrict __format, ...) __THROW; 

/* Maximum chars of output to write in MAXLEN. 和函数sprintf类似，但是更加安全，增加了__maxlen参数 */

extern int snprintf (char *__restrict __s, size_t __maxlen,

    __const char *__restrict __format, ...) 

/* Read a character from STREAM.

从流中读取字符

   These functions are possible cancellation points and therefore not

   marked with __THROW.  */

extern int fgetc (FILE *__stream);

extern int getc (FILE *__stream); 

/* Write a character to STREAM.

向流中写入字符

   These functions are possible cancellation points and therefore not

   marked with __THROW.

   These functions is a possible cancellation point and therefore not

   marked with __THROW.  */

extern int fputc (int __c, FILE *__stream);

extern int putc (int __c, FILE *__stream); 

 

/* Get a newline-terminated string of finite length from STREAM.

读取一行，s为开始指针，n为缓存长度

   This function is a possible cancellation point and therefore not

   marked with __THROW.  */

extern char *fgets (char *__restrict __s, int __n, FILE *__restrict __stream)

     __wur;

/* 向流中写入字符串 */ 

extern int fputs (__const char *__restrict __s, FILE *__restrict __stream); 

/* Push a character back onto the input buffer of STREAM.

向流中回退一个字符

   This function is a possible cancellation points and therefore not

   marked with __THROW.  */

extern int ungetc (int __c, FILE *__stream); 

/***************************二进制读取写入******************************************/ 

/* Read chunks of generic data from STREAM.

   This function is a possible cancellation points and therefore not

   marked with __THROW.  */

extern size_t fread (void *__restrict __ptr, size_t __size,

    size_t __n, FILE *__restrict __stream) __wur;

/* Write chunks of generic data to STREAM.

ptr读取缓存区开始位置，size：单位的长度，n读取数量

   This function is a possible cancellation points and therefore not

   marked with __THROW.  */

extern size_t fwrite (__const void *__restrict __ptr, size_t __size,

     size_t __n, FILE *__restrict __s); 

/********************************流指针操作**************************************/

/* Seek to a certain position on STREAM.

   This function is a possible cancellation point and therefore not

   marked with __THROW.  */

extern int fseek (FILE *__stream, long int __off, int __whence);

/* Return the current position of STREAM.

   This function is a possible cancellation point and therefore not

   marked with __THROW.  */

extern long int ftell (FILE *__stream) __wur;

/* Rewind to the beginning of STREAM.

将流指针回到文件开始

   This function is a possible cancellation point and therefore not

   marked with __THROW.  */

extern void rewind (FILE *__stream); 

/*****************************另外和文件锁相关的函数************************************/