VC读写函数详解(针对文件)

VC读写函数详解1．当前文件指针位置获取函数long ftell( FILE *stream );参数：stream 文件指针返回值：当前文件指针的位置实例：#include <stdio.h>FILE *stream;void main( void ){long position;char list[100];if( (stream = fopen( "ftell.c", "rb" )) != NULL ){/* Move the pointer by reading data: */fread( list, sizeof( char ), 100, stream );/* Get position after read: */position = ftell( stream );printf( "Position after trying to read 100 bytes: %ld\n",position );fclose( stream );}}输出：Position after trying to read 100 bytes: 1002．文件的打开函数FILE *fopen( const char *filename, const char *mode );FILE *_wfopen( const wchar_t *filename, const wchar_t *mode );参数：filename 文件的名称mode 打开文件的模式返回值：成功的打开文件的话返回文件的指针否则返回NULL表示打开文件错误注："r"只读方式打开"w"以写入方式打开"a"从文件的尾端写入数据，要是文件不存在则创建后写入数据"r+"以读写方式打开（文件必须存在）"w+"打开一个可以读写的文件，如果该文件存在则覆盖写入"a+"打开文件并追加写入源于<stdio.h>实例：#include <stdio.h>FILE *stream, *stream2;void main( void ){int numclosed;/* Open for read (will fail if file "data" does not exist) */if( (stream = fopen( "data", "r" )) == NULL )printf( "The file 'data' was not opened\n" );elseprintf( "The file 'data' was opened\n" );/* Open for write */if( (stream2 = fopen( "data2", "w+" )) == NULL )printf( "The file 'data2' was not opened\n" );elseprintf( "The file 'data2' was opened\n" );/* Close stream */if( fclose( stream ) )printf( "The file 'data' was not closed\n" );/* All other files are closed: */numclosed = _fcloseall( );printf( "Number of files closed by _fcloseall: %u\n", numclosed ); }输出：The file 'data' was openedThe file 'data2' was openedNumber of files closed by _fcloseall: 13.文件读取函数size_t fread( void *buffer, size_t size, size_t count, FILE *stream ) 参数： buffer 文件读取缓冲区 size 读取数据的类型 count 读取数据的个数stream 文件指针返回值：实际读取的数据个数源于<stdio.h>例子：FILE* fp;char* buffer=new char[1024];long realLength=fread(buffer,sizeof(char),1024,fp);////处理过程//delete buffer;fclose(fp);4.文件的写入函数size_t fwrite( const void *buffer, size_t size, size_t count, FILE*stream );参数： buffer 所要写入文件的缓冲区 size 写入数据的类型 count 写入数据的个数 stream 文件指针返回值：实际写入的数据个数源于<stdio.h>实例：#include <stdio.h>void main( void ){FILE *stream;char list[30];int i, numread, numwritten;/* Open file in text mode: */if( (stream = fopen( "fread.out", "w+t" )) != NULL ){for ( i = 0; i < 25; i++ )list[i] = (char)('z' - i);/* Write 25 characters to stream */numwritten = fwrite( list, sizeof( char ), 25, stream );printf( "Wrote %d items\n", numwritten );fclose( stream );}elseprintf( "Problem opening the file\n" );if( (stream = fopen( "fread.out", "r+t" )) != NULL ){/* Attempt to read in 25 characters */numread = fread( list, sizeof( char ), 25, stream );printf( "Number of items read = %d\n", numread );printf( "Contents of buffer = %.25s\n", list );fclose( stream );}elseprintf( "File could not be opened\n" );}输出：Wrote 25 itemsNumber of items read = 25Contents of buffer = zyxwvutsrqponmlkjihgfedcb5.文件指针搜索函数int fseek( FILE *stream, long offset, int origin )参数： stream 文件指针 offset 从当前指针开始的偏移量 origin 文件指针当前的位置返回值：成功返回0 否则返回非零值注：指针移动的时候是按字节移动的，要是成功的话文件的指针将指向当前搜索到的位置origin 可以的取值在 stdio.h已经定义如下：SEEK_CUR当前的文件指针SEEK_END文件结束SEEK_SET文件的开始源于<stdio.h>实例：#include <stdio.h>void main( void ){FILE *stream;char line[81];int result;stream = fopen( "fseek.out", "w+" );if( stream == NULL )printf( "The file fseek.out was not opened\n" );else{fprintf( stream, "The fseek begins here: ""This is the file 'fseek.out'.\n" );result = fseek( stream, 23L, SEEK_SET);if( result )printf( "Fseek failed" );else{printf( "File pointer is set to middle of first line.\n" ); fgets( line, 80, stream );printf( "%s", line );}fclose( stream );}}输出：File pointer is set to middle of first line.This is the file 'fseek.out'.6.按固定的格式写入数据函数int fprintf( FILE *stream, const char *format [, argument ]...)int fwprintf( FILE *stream, const wchar_t *format [, argument ]...) 参数：stream 文件指针format 按照一定的格式argument 可选参数列表返回值：fprintf 返回实际写入的字节数.fwprintf返回实际写入的wchar_t 的字节数源于<stdio.h>实例：#include <stdio.h>#include <process.h>FILE *stream;void main( void ){int i = 10;double fp = 1.5;char s[] = "this is a string";char c = '\n';stream = fopen( "fprintf.out", "w" );fprintf( stream, "%s%c", s, c );fprintf( stream, "%d\n", i );fprintf( stream, "%f\n", fp );fclose( stream );system( "type fprintf.out" );}输出：this is a string101.5000007．按固定的格式读入数据函数int fscanf( FILE *stream, const char *format [, argument ]... )int fwscanf( FILE *stream, const wchar_t *format [, argument ]... ) 参数：stream 文件指针format 按照一定的格式argument 可选参数列表返回值：fscanf 返回实际读入的字节数.fwscanf返回实际读入的wchar_t 的字节数如果返回值为 0 则说明没有被赋值如果有文件结束或是异常的IO错误时返回 EOF(宏定义)源于<stdio.h>实例：#include <stdio.h>FILE *stream;void main( void ){long l;float fp;char s[81];char c;stream = fopen( "fscanf.out", "w+" );if( stream == NULL )printf( "The file fscanf.out was not opened\n" );else{fprintf( stream, "%s %ld %f%c", "a-string",65000, 3.14159, 'x' );/* Set pointer to beginning of file: */fseek( stream, 0L, SEEK_SET );/* Read data back from file: */fscanf( stream, "%s", s );fscanf( stream, "%ld", &l );fscanf( stream, "%f", &fp );fscanf( stream, "%c", &c );/* Output data read: */printf( "%s\n", s );printf( "%ld\n", l );printf( "%f\n", fp );printf( "%c\n", c );fclose( stream );}}输出：a-string650003.141590X8．文件指针的定位和获取int fsetpos( FILE *stream, const fpos_t *pos );int fgetpos( FILE *stream, const fpos_t *pos );参数：stream 目标文件指针pos 文件指针的位置返回值：设置指针位置成功的话fsetpos返回0 否则返回一个非零的数获得指针位置成功的话fgetpos返回0 否则返回一个非零的数源于<stdio.h>实例：#include <stdio.h>void main( void ){FILE *stream;fpos_t pos;char buffer[20];if( (stream = fopen( "fgetpos.c", "rb" )) == NULL )printf( "Trouble opening file\n" );else{/* Read some data and then check the position. */fread( buffer, sizeof( char ), 10, stream );if( fgetpos( stream, &pos ) != 0 )printf( "fgetpos error" );else{fread( buffer, sizeof( char ), 10, stream );printf( "10 bytes at byte %I64d: %.10s\n", pos, buffer ); }/* Set a new position and read more data */pos = 140;if( fsetpos( stream, &pos ) != 0 )printf( "fsetpos error" );fread( buffer, sizeof( char ), 10, stream );printf( "10 bytes at byte %I64d: %.10s\n", pos, buffer );fclose( stream );}}输出：10 bytes at byte 10: .C: This p10 bytes at byte 140: .C and the9.文件指针重新定位到开始void rewind( FILE *stream )参数：stream 文件指针返回值：无注：执行完本函数后，文件的指针将返回到开始位置实例：#include <stdio.h>void main( void ){FILE *stream;int data1, data2;data1 = 1;data2 = -37;if( (stream = fopen( "rewind.out", "w+" )) != NULL ){fprintf( stream, "%d %d", data1, data2 );printf( "The values written are: %d and %d\n", data1, data2 ); rewind( stream );fscanf( stream, "%d %d", &data1, &data2 );printf( "The values read are: %d and %d\n", data1, data2 );fclose( stream );}}输出：The values written are: 1 and -37The values read are: 1 and -3710．取得文件指针所指的行char *fgets( char *string, int n, FILE *stream );int fputs( const char *string, FILE *stream );参数：fgets 的string 保存到的字符串缓冲，而fputs 的string 表示要写入的字符串n表示从文件中读出的字符串不超过 n-1个字符，在读入的最后一个字符后加上串结束标志'\0'stream 文件指针返回值：成功的话返回字符数组的首地址否则返回NULL源于<stdio.h>实例：#include <stdio.h>void main( void ){FILE *stream;char line[100];if( (stream = fopen( "fgets.c", "r" )) != NULL ){if( fgets( line, 100, stream ) == NULL)printf( "fgets error\n" );elseprintf( "%s", line);fclose( stream );}fputs( "Hello world from fputs.\n", stdout );}输出：This program uses fgets to displayHello world from fputs.11．关闭文件函数int _fcloseall( void )int fclose( FILE *stream )参数：stream 文件指针返回值：fclose成功关闭返回 0 否则返回EOF 表示错误_fcloseall 成功返回总共关闭的文件数否则的话返回EOF 表示错误实例：#include <stdio.h>FILE *stream, *stream2;void main( void ){int numclosed;/* Open for read (will fail if file "data" does not exist) */if( (stream = fopen( "data", "r" )) == NULL )printf( "The file 'data' was not opened\n" );elseprintf( "The file 'data' was opened\n" );/* Open for write */if( (stream2 = fopen( "data2", "w+" )) == NULL )printf( "The file 'data2' was not opened\n" );elseprintf( "The file 'data2' was opened\n" );/* Close stream */if( fclose( stream ) )printf( "The file 'data' was not closed\n" );/* All other files are closed: */numclosed = _fcloseall( );printf( "Number of files closed by _fcloseall: %u\n", numclosed ); }输出：The file 'data' was openedThe file 'data2' was openedNumber of files closed by _fcloseall: 1完。