VC读写函数详解(针对文件)

1、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 FILE *stream;void main( void ) long position; char list100; if( (stream = fopen( ftell.c, rb ) != NULL ) /* Move the pointer by reading data: */ fread( list, sizeof( char ), 100, stream ); /* Get position after re

2、ad: */ position = ftell( stream ); printf( Position after trying to read 100 bytes: %ldn, 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：filena

3、me 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实例：#include FILE *stream, *stream2;void main( void ) int numclosed; /* Open for read (will fail if file data does not exist) */ if( (str

4、eam = fopen( data, r ) = NULL ) printf( The file data was not openedn ); else printf( The file data was openedn ); /* Open for write */ if( (stream2 = fopen( data2, w+ ) = NULL ) printf( The file data2 was not openedn ); else printf( The file data2 was openedn ); /* Close stream */ if( fclose( strea

5、m ) ) printf( The file data was not closedn ); /* All other files are closed: */ numclosed = _fcloseall( ); printf( Number of files closed by _fcloseall: %un, 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, si

6、ze_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例子：FILE* fp;char* buffer=new char1024;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

7、, 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实例：#include void main( void ) FILE *stream; char list30; int i, numread, numwritten; /* Open file in text mode: */ if( (stream = fopen( fread.out, w+t ) != NULL ) for ( i = 0; i 25; i+ ) listi = (char)(z - i)

8、; /* Write 25 characters to stream */ numwritten = fwrite( list, sizeof( char ), 25, stream ); printf( Wrote %d itemsn, numwritten ); fclose( stream ); else printf( Problem opening the filen ); if( (stream = fopen( fread.out, r+t ) != NULL ) /* Attempt to read in 25 characters */ numread = fread( li

9、st, sizeof( char ), 25, stream ); printf( Number of items read = %dn, numread ); printf( Contents of buffer = %.25sn, list ); fclose( stream ); else printf( File could not be openedn );输出：Wrote 25 itemsNumber of items read = 25Contents of buffer = zyxwvutsrqponmlkjihgfedcb5.文件指针搜索函数int fseek( FILE *

10、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 文件的开始源于实例：#include void main( void ) FILE *stream; char line81; int result; stream = fopen( f

11、seek.out, w+ ); if( stream = NULL ) printf( The file fseek.out was not openedn ); 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 ); fg

12、ets( 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

13、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 的字节数源于实例：#include #include 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, %dn, i ); fprintf( stream, %fn

14、, 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wcha

15、r_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)源于实例：#include FILE *stream;void main( void ) long l; float fp; char s81; char c; stream = fopen( fscanf.out, w+ ); if( stream = NULL ) printf( The file fscanf.out was not openedn ); else fprintf( stream, %s %ld %f%c, a-string, 65000, 3.14159, x )

16、; /* 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( %sn, s ); printf( %ldn, l ); printf( %fn, fp ); printf( %c

17、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实例：#include void main( void ) FILE *stream; fpo

18、s_t pos; char buffer20; if( (stream = fopen( fgetpos.c, rb ) = NULL ) printf( Trouble opening filen ); 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 ), 1

19、0, stream ); printf( 10 bytes at byte %I64d: %.10sn, 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: %.10sn, pos, buffer ); fclose( stream );

20、 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 void main( void ) FILE *stream; int data1, data2; data1 = 1; data2 = -37; if( (stream = fopen( rewind.out, w+ ) != NULL ) fprintf( stream,

21、%d %d, data1, data2 ); printf( The values written are: %d and %dn, data1, data2 ); rewind( stream ); fscanf( stream, %d %d, &data1, &data2 ); printf( The values read are: %d and %dn, 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

22、*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0stream 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 源于实例：#include void main( void ) FILE *stream; char line100; if( (stream = fo

23、pen( fgets.c, r ) != NULL ) if( fgets( line, 100, stream ) = NULL) printf( fgets errorn ); else printf( %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