文件操作.docx
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文件操作
文件操作
1.文件的读取与写入
新建一个MFC单文档应用程序（工程名取:
File）,打开菜单资源新建一个文件菜单，并在其下添加以下菜单项（ID:
IDM_FILE_READ,Caption:
读取）和（ID:
IDM_FILE_WRITE,Caption:
写入），并分别给它们添加CFileView类上的命令响应，编辑：
void CFileView:
:
OnFileRead（）
{
// TODO:
Add your command handler code here
FILE *pFile=fopen（"1.txt","r"）;//为了读取而打开一个文件
// char ch[100];
// memset（ch,0,100）;
//将字符数组中所有的数据都设为零,这样读取时，就只读取到有字符的位置
// fread（ch,1,100,pFile）;//读取文件
// MessageBox（ch）;
char *pBuf;
fseek（pFile,0,SEEK_END）;//将文件的指针移到文件的末尾
int len=ftell（pFile）;//获取文件的大小
pBuf=new char[len+1];//根据文件的大小分配内存，多分配一个是为了存取'\0'
rewind（pFile）;//这个函数可以将文件指针移到文件的开始处
fread（pBuf,1,len,pFile）;//读取len所表示的文件的长度的数据
pBuf[len]=0;//将数组的最后个元素设置为0，因为数据索引是从0开始的，所以len表示最后一个
MessageBox（pBuf）;
fclose（pFile）;
//fflush（pFile）;//刷新缓冲区，让缓冲区的数据写入文件
}
void CFileView:
:
OnFileWrite（）
{
// TODO:
Add your command handler code here
FILE *pFile=fopen（"1.txt","w"）;//为了写入而打开一个文件
fwrite（"",1,strlen（""）,pFile）;
//把字符串写入文件
//fwrite（"",1,strlen（""）+1,pFile）;
//为了让读取到指定字符就结束，+1是在文件中多写入一个字节，多写的字节为空，默认也是0，就是字符串的结尾
//fwrite（"",1,strlen（""）,pFile）;
//还可以再次写入，位置是上次写入后文件指针所在的位置
//fseek（pFile,0,SEEK_SET）;//将文件的指针位置设为零
//fwrite（"ftp:
//10.6.17.19",1,strlen（"ftp:
//10.6.17.19"）,pFile）;
//fclose（pFile）;//关闭文件，表明文件的写操作已完成，缓冲区内容将写入文件
fflush（pFile）;//刷新缓冲区，让缓冲区的数据写入文件
}
2.文件写入时经常会碰到的问题
void CFileView:
:
OnFileWrite（）
{
//FILE *pFile=fopen（"2.txt","w"）;
FILE *pFile=fopen（"2.txt","wb"）;
char ch[3];
ch[0]='a';
ch[1]=10;//10实际上指换行符
ch[2]='b';
fwrite（ch,1,3,pFile）;//写入
fclose（pFile）;
//运行可以发现在文件里写入了4个字节，回车符13占了两个字节
//转换成十六制可以发现：
61 0D 0A 62 ;a..b
}
void CFileView:
:
OnFileRead（）
{
//FILE *pFile=fopen（"2.txt","r"）;//缺省是按文本方式（t）打开
FILE *pFile=fopen（"2.txt","rb"）;//以二进制方式（b）打开
char ch[100];
fread（ch,1,3,pFile）;//读取文件
ch[3]=0;
MessageBox（ch）;
fclose（pFile）;
//以文本方式写入的文件
//以文本方式打开文件用3个字节读取发现仍然可以读出来
//以二进制方式用3个字符打开不能将b读出，只能读到61 0D 0A
//以二进制方式写入的文件
//以二进制方式用3个字符打开能将b读出
}
二进制文件和文本文件
3.一个问题
98341，将这个整数保存到文件中，要求在以记事本程序打开文件时，显示的是98341。
void CFileView:
:
OnFileWrite（）
{
FILE *pFile=fopen（"3.txt","w"）;
int i=98341;
char ch[5];
/* ch[0]=9+48;//以ASCII码存进去
ch[1]=8+48;
ch[2]=3+48;
ch[3]=4+48;
ch[4]=1+48;
*/
itoa（i,ch,10）;
//fwrite（&i,4,1,pFile）;
fwrite（ch,1,5,pFile）;
fclose（pFile）;
}
===============================================
fopen,_wfopen
Openafile.
FILE*fopen（constchar*filename,constchar*mode）;
FILE*_wfopen（constwchar_t*filename,constwchar_t*mode）;
Function
RequiredHeader
Compatibility
fopen
ANSI,Win95,WinNT
_wfopen
or
WinNT
Foradditionalcompatibilityinformation,seeCompatibilityintheIntroduction.
Libraries
LIBC.LIB
Singlethreadstaticlibrary,retailversion
LIBCMT.LIB
Multithreadstaticlibrary,retailversion
MSVCRT.LIB
ImportlibraryforMSVCRT.DLL,retailversion
Thec,n,andtmodeoptionsareMicrosoftextensionsforfopenand_fdopenandshouldnotbeusedwhereANSIportabilityisdesired.
ReturnValue
Eachofthesefunctionsreturnsapointertotheopenfile.Anullpointervalueindicatesanerror.
Parameters
filename
Filename
mode
Typeofaccesspermitted
Remarks
Thefopenfunctionopensthefilespecifiedbyfilename._wfopenisawide-characterversionoffopen;theargumentsto_wfopenarewide-characterstrings._wfopenandfopenbehaveidenticallyotherwise.
Generic-TextRoutineMappings
TCHAR.HRoutine
_UNICODE&_MBCSNotDefined
_MBCSDefined
_UNICODEDefined
_tfopen
fopen
fopen
_wfopen
Thecharacterstringmodespecifiesthetypeofaccessrequestedforthefile,asfollows:
"r"
Opensforreading.Ifthefiledoesnotexistorcannotbefound,thefopencallfails.
"w"
Opensanemptyfileforwriting.Ifthegivenfileexists,itscontentsaredestroyed.
"a"
Opensforwritingattheendofthefile（appending）withoutremovingtheEOFmarkerbeforewritingnewdatatothefile;createsthefilefirstifitdoesn’texist.
"r+"
Opensforbothreadingandwriting.（Thefilemustexist.）
"w+"
Opensanemptyfileforbothreadingandwriting.Ifthegivenfileexists,itscontentsaredestroyed.
"a+"
Opensforreadingandappending;theappendingoperationincludestheremovaloftheEOFmarkerbeforenewdataiswrittentothefileandtheEOFmarkerisrestoredafterwritingiscomplete;createsthefilefirstifitdoesn’texist.
Whenafileisopenedwiththe"a"or"a+"accesstype,allwriteoperationsoccurattheendofthefile.Thefilepointercanberepositionedusingfseekorrewind,butisalwaysmovedbacktotheendofthefilebeforeanywriteoperationiscarriedout.Thus,existingdatacannotbeoverwritten.
The"a"modedoesnotremovetheEOFmarkerbeforeappendingtothefile.Afterappendinghasoccurred,theMS-DOSTYPEcommandonlyshowsdatauptotheoriginalEOFmarkerandnotanydataappendedtothefile.The"a+"modedoesremovetheEOFmarkerbeforeappendingtothefile.Afterappending,theMS-DOSTYPEcommandshowsalldatainthefile.The"a+"modeisrequiredforappendingtoastreamfilethatisterminatedwiththeCTRL+ZEOFmarker.
Whenthe"r+","w+",or"a+"accesstypeisspecified,bothreadingandwritingareallowed（thefileissaidtobeopenfor“update”）.However,whenyouswitchbetweenreadingandwriting,theremustbeaninterveningfflush,fsetpos,fseek,orrewindoperation.Thecurrentpositioncanbespecifiedforthefsetposorfseekoperation,ifdesired.
Inadditiontotheabovevalues,thefollowingcharacterscanbeincludedinmodetospecifythetranslationmodefornewlinecharacters:
t
Openintext（translated）mode.Inthismode,CTRL+Zisinterpretedasanend-of-filecharacteroninput.Infilesopenedforreading/writingwith"a+",fopenchecksforaCTRL+Zattheendofthefileandremovesit,ifpossible.ThisisdonebecauseusingfseekandftelltomovewithinafilethatendswithaCTRL+Z,maycausefseektobehaveimproperlyneartheendofthefile.
Also,intextmode,carriagereturn–linefeedcombinationsaretranslatedintosinglelinefeedsoninput,andlinefeedcharactersaretranslatedtocarriagereturn–linefeedcombinationsonoutput.WhenaUnicodestream-I/Ofunctionoperatesintextmode（thedefault）,thesourceordestinationstreamisassumedtobeasequenceofmultibytecharacters.Therefore,theUnicodestream-inputfunctionsconvertmultibytecharacterstowidecharacters（asifbyacalltothembtowcfunction）.Forthesamereason,theUnicodestream-outputfunctionsconvertwidecharacterstomultibytecharacters（asifbyacalltothewctombfunction）.
b
Openinbinary（untranslated）mode;translationsinvolvingcarriage-returnandlinefeedcharactersaresuppressed.
Iftorbisnotgiveninmode,thedefaulttranslationmodeisdefinedbytheglobalvariable_fmode.Iftorbisprefixedtotheargument,thefunctionfailsandreturnsNULL.
FormoreinformationaboutusingtextandbinarymodesinUnicodeandmultibytestream-I/O,seeTextandBinaryModeFileI/OandUnicodeStreamI/OinTextandBinaryModes.
c
Enablethecommitflagfortheassociatedfilenamesothatthecontentsofthefilebufferarewrittendirectlytodiskifeitherfflushor_flushalliscalled.
n
Resetthecommitflagfortheassociatedfilenameto“no-commit.”Thisisthedefault.ItalsooverridestheglobalcommitflagifyoulinkyourprogramwithCOMMODE.OBJ.Theglobalcommitflagdefaultis“no-commit”unlessyouexplicitlylinkyourprogramwithCOMMODE.OBJ.
Validcharactersforthemodestringusedinfopenand_fdopencorrespondtooflagargumentsusedin_openand_sopen,asfollows.
CharactersinmodeString
EquivalentoflagValuefor_open/_sopen
a
_O_WRONLY|_O_APPEND（usually_O_WRONLY|_O_CREAT|_O_APPEND）
a+
_O_RDWR|_O_APPEND（usually_O_RDWR|_O_APPEND|_O_CREAT）
r
_O_RDONLY
r+
_O_RDWR
w
_O_WRONLY（usually_O_WRONLY|_O_CREAT|_O_TRUNC）
w+
_O_RDWR（usually_O_RDWR|_O_CREAT|_O_TRUNC）
b
_O_BINARY
t
_O_TEXT
c
None
n
None
Example
/*FOPEN.C:
Thisprogramopensfilesnamed"data"
*and"data2".It usesfclosetoclose"data"and
*_fclosealltocloseallremainingfiles.
*/
#include
FILE*stream,*stream2;
voidmain（void）
{
intnumclosed;
/*Openforread（willfailiffile"data"doesnotexist）*/
if（（stream =fopen（"data","r"））==NULL）
printf（"Thefile'data'wasnotopened\n"）;
else
printf（"Thefile'data'wasopened\n"）;
/*Openforwrite*/
if（（stream2=fopen（"data2","w+"））==NULL）
printf（"Thefile'data2'wasnotopened\n"）;
else
printf（"Thefile'data2'wasopened\n"）;
/*Closestream*/
if（fclose（stream））
printf（"Thefile'data'wasnotclosed\n"）;
/*Allotherfilesareclosed:
*/
numclosed=_fcloseall（）;
printf（"Numberoffilesclosedby_fcloseall:
%u\n",numclosed）;
}
Output
Thefile'data'wasopened
Thefile'data2'wasopened
Numberoffilesclosedby_fcloseall:
1
===============================================
4.C++中对文件操作
void CFileView:
:
OnFileWrite（）
{
ofstream ofs（"4.txt"）;//构造一个对象传递文件名4.txt
//C++中写入文件可以用这个类
ofs.write（"",strlen（""））;
ofs.close（）;
}
void CFileView:
:
OnFileRead（）
{
ifstream ifs（"4.txt"）;//读入一个文件用这个类
char ch[100];
memset（ch,0,100）;//将字符数组中的内存都设为零
ifs.read（ch,100）;
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