1. io操作实例
2. io函数分析
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); }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************************************/
