一般地，在C语言或C++中，会把用来#include的文件的扩展名叫 .h，称其为头文件。 #include文件的目的就是把多个编译单元（也就是c或者cpp文件）公用的内容，单独放在一个文件里减少整体代码尺寸；或者提供跨工程公共代码。
#include <stdio.h>
stdio 就是指 “standard input & output"（标准输入输出）
简介
stdio .h 头文件定义了三个变量类型、一些宏和各种函数来执行输入和输出。
库变量
下面是头文件 stdio.h 中定义的变量类型：
| 序号 | 变量 & 描述 |
|---|---|
| 1 | size_t 这是无符号整数类型，它是 sizeof 关键字的结果。 |
| 2 | FILE 这是一个适合存储文件流信息的对象类型。 |
| 3 | fpos_t 这是一个适合存储文件中任何位置的对象类型。 |
库宏
下面是头文件 stdio.h 中定义的宏：
| 序号 | 宏 & 描述 |
|---|---|
| 1 | NULL 这个宏是一个空指针常量的值。 |
| 2 | _IOFBF、_IOLBF 和 _IONBF 这些宏扩展了带有特定值的整型常量表达式，并适用于 setvbuf 函数的第三个参数。 |
| 3 | BUFSIZ 这个宏是一个整数，该整数代表了 setbuf 函数使用的缓冲区大小。 |
| 4 | EOF 这个宏是一个表示已经到达文件结束的负整数。 |
| 5 | FOPEN_MAX 这个宏是一个整数，该整数代表了系统可以同时打开的文件数量。 |
| 6 | FILENAME_MAX 这个宏是一个整数，该整数代表了字符数组可以存储的文件名的最大长度。如果实现没有任何限制，则该值应为推荐的最大值。 |
| 7 | L_tmpnam 这个宏是一个整数，该整数代表了字符数组可以存储的由 tmpnam 函数创建的临时文件名的最大长度。 |
| 8 | SEEK_CUR、SEEK_END 和 SEEK_SET 这些宏是在These macros are used in the fseek 函数中使用，用于在一个文件中定位不同的位置。 |
| 9 | TMP_MAX 这个宏是 tmpnam 函数可生成的独特文件名的最大数量。 |
| 10 | stderr、stdin 和 stdout 这些宏是指向 FILE 类型的指针，分别对应于标准错误、标准输入和标准输出流。 |
库函数
下面是头文件 stdio.h 中定义的函数：
为了更好地理解函数，请按照下面的序列学习这些函数，因为第一个函数中创建的文件会在后续的函数中使用到。
标准函数
int getchar()//从标准输入设备读入一个字符 int putchar()//向标准输出设备写出一个字符 int scanf(char*format[,argument…])//从标准输入设备读入格式化后的数据 int printf(char*format[,argument…])//向标准输出设备输出格式化字符串 char gets(char*string)//从标准输入设备读入一个字符串 int puts(char*string)//向标准输出设备输出一个字符串 int sprintf(char*string,char*format[,…])//把格式化的数据写入某个字符串缓冲区
文件内容
文件说明
/* *stdio.h *ThisfilehasnocopyrightassignedandisplacedinthePublicDomain. *Thisfileisapartofthemingw-runtimepackage. *Nowarrantyisgiven;refertothefileDISCLAIMERwithinthepackage. * *Definitionsoftypesandprototypesoffunctionsforstandardinputand *output. * *NOTE:ThefilemanipulationfunctionsprovidedbyMicrosoftseemto *workwitheitherslash(/)orbackslash()asthedirectoryseparator. * */
宏定义
#ifndef_STDIO_H_ #define_STDIO_H_ /*Alltheheadersincludethisfile.*/ #include<_mingw.h> #ifndefRC_INVOKED #define__need_size_t #define__need_NULL #define__need_wchar_t #define__need_wint_t #include<stddef.h> #define__need___va_list #include<stdarg.h> #endif/*NotRC_INVOKED*/ /*Flagsfortheiobufstructure*/ #define_IOREAD1/*currentlyreading*/ #define_IOWRT2/*currentlywriting*/ #define_IORW0x0080/*openedas"r+w"*/ /* *Thethreestandardfilepointersprovidedbytheruntimelibrary. *NOTE:Thesewillgotothebit-bucketsilentlyinGUIapplications! */ #defineSTDIN_FILENO0 #defineSTDOUT_FILENO1 #defineSTDERR_FILENO2 /*Returnedbyvariousfunctionsonendoffileconditionorerror.*/ #defineEOF(-1) /* *Themaximumlengthofafilename.YoushoulduseGetVolumeInformation *insteadofthisconstant.Buthey,thisworks. *Alsodefinedinio.h. */ #ifndefFILENAME_MAX #defineFILENAME_MAX(260) #endif /* *Themaximumnumberoffilesthatmaybeopenatonce.Ihavesetthisto *aconservativenumber.Theactualvaluemaybehigher. */ #defineFOPEN_MAX(20) /*Aftercreatingthismanynames,tmpnamandtmpfilereturnNULL*/ #defineTMP_MAX32767 /* *Tmpnam,tmpfileand,sometimes,_tempnamtrytocreate *tempfilesintherootdirectoryofthecurrentdrive *(notinpwd,assuggestedbysomeolderMSdoc's). *RedefiningthesemacrosdoesnoteffecttheCRTfunctions. */ #define_P_tmpdir"\" #ifndef__STRICT_ANSI__ #defineP_tmpdir_P_tmpdir #endif #define_wP_tmpdirL"\" /* *Themaximumsizeofname(includingNUL)thatwillbeputintheuser *suppliedbuffercaNamefortmpnam. *Inferredfromthesizeofthestaticbufferreturnedbytmpnam *whenpassedaNULLargument.Mayactuallybesmaller. */ #defineL_tmpnam(16) #define_IOFBF0x0000/*fullbuffered*/ #define_IOLBF0x0040/*linebuffered*/ #define_IONBF0x0004/*notbuffered*/ #define_IOMYBUF0x0008/*stdiomalloc()'dbuffer*/ #define_IOEOF0x0010/*EOFreachedonread*/ #define_IOERR0x0020/*I/Oerrorfromsystem*/ #define_IOSTRG0x0040/*Strangeornofiledescriptor*/ #ifdef_POSIX_SOURCE #define_IOAPPEND0x0200 #endif /* *Thebuffersizeasusedbysetbufsuchthatitisequivalentto *(void)setvbuf(fileSetBuffer,caBuffer,_IOFBF,BUFSIZ). */ #defineBUFSIZ512 /*ConstantsfornOriginindicatingthepositionrelativetowhichfseek *setsthefileposition.Enclosedinifdefsbecauseio.hcouldalso *definethem.(Thoughnotanymoresinceio.hincludesthisfilenow.)*/ #ifndefSEEK_SET #defineSEEK_SET(0) #endif #ifndefSEEK_CUR #defineSEEK_CUR(1) #endif #ifndefSEEK_END #defineSEEK_END(2) #endif #ifndefRC_INVOKED #ifndef__VALIST #ifdef__GNUC__ #define__VALIST__gnuc_va_list #else #define__VALISTchar* #endif #endif/*defined__VALIST*/ /* *ThestructureunderlyingtheFILEtype. * *Somebelievethatnobodyintheirrightmindshouldmakeuseofthe *internalsofthisstructure.ProvidedbyPedroA.ArandaGutiirrez */ #ifndef_FILE_DEFINED #define_FILE_DEFINED
结构体定义
typedefstruct_iobuf { char*_ptr; int_cnt; char*_base; int_flag; int_file; int_charbuf; int_bufsiz; char*_tmpfname; }FILE; #endif/*Not_FILE_DEFINED*/ /* *Thestandardfilehandles */ #ifndef__DECLSPEC_SUPPORTED externFILE(*_imp___iob)[];/*ApointertoanarrayofFILE*/ #define_iob(*_imp___iob)/*AnarrayofFILE*/ #else/*__DECLSPEC_SUPPORTED*/ __MINGW_IMPORTFILE_iob[];/*AnarrayofFILEimportedfromDLL.*/ #endif/*__DECLSPEC_SUPPORTED*/ #definestdin(&_iob[STDIN_FILENO]) #definestdout(&_iob[STDOUT_FILENO]) #definestderr(&_iob[STDERR_FILENO])
操作函数定义
#ifdef__cplusplus extern"C"{ #endif /* *FileOperations */ _CRTIMPFILE*__cdeclfopen(constchar*,constchar*); _CRTIMPFILE*__cdeclfreopen(constchar*,constchar*,FILE*); _CRTIMPint__cdeclfflush(FILE*); _CRTIMPint__cdeclfclose(FILE*); /*MSputsremove&rename(butnotwideversions)inio.halso*/ _CRTIMPint__cdeclremove(constchar*); _CRTIMPint__cdeclrename(constchar*,constchar*); _CRTIMPFILE*__cdecltmpfile(void); _CRTIMPchar*__cdecltmpnam(char*); #ifndef__STRICT_ANSI__ _CRTIMPchar*__cdecl_tempnam(constchar*,constchar*); _CRTIMPint__cdecl_rmtmp(void); #ifndefNO_OLDNAMES _CRTIMPchar*__cdecltempnam(constchar*,constchar*); _CRTIMPint__cdeclrmtmp(void); #endif #endif/*__STRICT_ANSI__*/ _CRTIMPint__cdeclsetvbuf(FILE*,char*,int,size_t); _CRTIMPvoid__cdeclsetbuf(FILE*,char*); /* *FormattedOutput */ _CRTIMPint__cdeclfprintf(FILE*,constchar*,...); _CRTIMPint__cdeclprintf(constchar*,...); _CRTIMPint__cdeclsprintf(char*,constchar*,...); _CRTIMPint__cdecl_snprintf(char*,size_t,constchar*,...); _CRTIMPint__cdeclvfprintf(FILE*,constchar*,__VALIST); _CRTIMPint__cdeclvprintf(constchar*,__VALIST); _CRTIMPint__cdeclvsprintf(char*,constchar*,__VALIST); _CRTIMPint__cdecl_vsnprintf(char*,size_t,constchar*,__VALIST); #ifndef__NO_ISOCEXT/*externsinlibmingwex.a*/ int__cdeclsnprintf(char*s,size_tn,constchar*format,...); __CRT_INLINEint__cdecl vsnprintf(char*s,size_tn,constchar*format,__VALISTarg) {return_vsnprintf(s,n,format,arg);} int__cdeclvscanf(constchar*__restrict__,__VALIST); int__cdeclvfscanf(FILE*__restrict__,constchar*__restrict__, __VALIST); int__cdeclvsscanf(constchar*__restrict__, constchar*__restrict__,__VALIST); #endif /* *FormattedInput */ _CRTIMPint__cdeclfscanf(FILE*,constchar*,...); _CRTIMPint__cdeclscanf(constchar*,...); _CRTIMPint__cdeclsscanf(constchar*,constchar*,...); /* *CharacterInputandOutputFunctions */ _CRTIMPint__cdeclfgetc(FILE*); _CRTIMPchar*__cdeclfgets(char*,int,FILE*); _CRTIMPint__cdeclfputc(int,FILE*); _CRTIMPint__cdeclfputs(constchar*,FILE*); _CRTIMPchar*__cdeclgets(char*); _CRTIMPint__cdeclputs(constchar*); _CRTIMPint__cdeclungetc(int,FILE*); /*Traditionally,getcandputcaredefinedasmacros.butthe standarddoesn'tsaythattheymustbemacros. Weuseinlinefunctionsheretoallowthefastversions tobeusedinC++withnamespacequalification,eg.,::getc. _filbufand_flsbufarenotthread-safe.*/ _CRTIMPint__cdecl_filbuf(FILE*); _CRTIMPint__cdecl_flsbuf(int,FILE*); #if!defined_MT __CRT_INLINEint__cdeclgetc(FILE*__F) { return(--__F->_cnt>=0) ?(int)(unsignedchar)*__F->_ptr++ :_filbuf(__F); } __CRT_INLINEint__cdeclputc(int__c,FILE*__F) { return(--__F->_cnt>=0) ?(int)(unsignedchar)(*__F->_ptr++=(char)__c) :_flsbuf(__c,__F); } __CRT_INLINEint__cdeclgetchar(void) { return(--stdin->_cnt>=0) ?(int)(unsignedchar)*stdin->_ptr++ :_filbuf(stdin); } __CRT_INLINEint__cdeclputchar(int__c) { return(--stdout->_cnt>=0) ?(int)(unsignedchar)(*stdout->_ptr++=(char)__c) :_flsbuf(__c,stdout);} #else/*Uselibraryfunctions.*/ _CRTIMPint__cdeclgetc(FILE*); _CRTIMPint__cdeclputc(int,FILE*); _CRTIMPint__cdeclgetchar(void); _CRTIMPint__cdeclputchar(int); #endif /* *DirectInputandOutputFunctions */ _CRTIMPsize_t__cdeclfread(void*,size_t,size_t,FILE*); _CRTIMPsize_t__cdeclfwrite(constvoid*,size_t,size_t,FILE*); /* *FilePositioningFunctions */ _CRTIMPint__cdeclfseek(FILE*,long,int); _CRTIMPlong__cdeclftell(FILE*); _CRTIMPvoid__cdeclrewind(FILE*); #ifdef__USE_MINGW_FSEEK/*Theseareinlibmingwex.a*/ /* *Workaroundforlimitationsonwin9xwhereafilecontentsare *notzero'doutifyouseekpasttheendandthenwrite. */ int__cdecl__mingw_fseek(FILE*,long,int); int__cdecl__mingw_fwrite(constvoid*,size_t,size_t,FILE*); #definefseek(fp,offset,whence)__mingw_fseek(fp,offset,whence) #definefwrite(buffer,size,count,fp)__mingw_fwrite(buffer,size,count,fp) #endif/*__USE_MINGW_FSEEK*/ /* *Anopaquedatatypeusedforstoringfilepositions...Thecontentsof *thistypeareunknown,butwe(thecompiler)needtoknowthesize *becausetheprogrammerusingfgetposandfsetposwillbesettingaside *storageforfpos_tstructres.ActuallyItestedusingabytearrayand *itisfairlyevidentthatthefpos_ttypeisalong(inCRTDLL.DLL). *Perhapsanunsignedlong?TODO?It'sdefinitelya64-bitnumberin *MSVCRThowever,andfornow`longlong'willdo. */ #ifdef__MSVCRT__ typedeflonglongfpos_t; #else typedeflongfpos_t; #endif _CRTIMPint__cdeclfgetpos(FILE*,fpos_t*); _CRTIMPint__cdeclfsetpos(FILE*,constfpos_t*); /* *ErrorFunctions */ _CRTIMPint__cdeclfeof(FILE*); _CRTIMPint__cdeclferror(FILE*); #ifdef__cplusplus inlineint__cdeclfeof(FILE*__F) {return__F->_flag&_IOEOF;} inlineint__cdeclferror(FILE*__F) {return__F->_flag&_IOERR;} #else #definefeof(__F)((__F)->_flag&_IOEOF) #defineferror(__F)((__F)->_flag&_IOERR) #endif _CRTIMPvoid__cdeclclearerr(FILE*); _CRTIMPvoid__cdeclperror(constchar*); #ifndef__STRICT_ANSI__ /* *Pipes */ _CRTIMPFILE*__cdecl_popen(constchar*,constchar*); _CRTIMPint__cdecl_pclose(FILE*); #ifndefNO_OLDNAMES _CRTIMPFILE*__cdeclpopen(constchar*,constchar*); _CRTIMPint__cdeclpclose(FILE*); #endif /* *OtherNonANSIfunctions */ _CRTIMPint__cdecl_flushall(void); _CRTIMPint__cdecl_fgetchar(void); _CRTIMPint__cdecl_fputchar(int); _CRTIMPFILE*__cdecl_fdopen(int,constchar*); _CRTIMPint__cdecl_fileno(FILE*); _CRTIMPint__cdecl_fcloseall(void); _CRTIMPFILE*__cdecl_fsopen(constchar*,constchar*,int); #ifdef__MSVCRT__ _CRTIMPint__cdecl_getmaxstdio(void); _CRTIMPint__cdecl_setmaxstdio(int); #endif #ifndef_NO_OLDNAMES _CRTIMPint__cdeclfgetchar(void); _CRTIMPint__cdeclfputchar(int); _CRTIMPFILE*__cdeclfdopen(int,constchar*); _CRTIMPint__cdeclfileno(FILE*); #endif/*Not_NO_OLDNAMES*/ #define_fileno(__F)((__F)->_file) #ifndef_NO_OLDNAMES #definefileno(__F)((__F)->_file) #endif #ifdefined(__MSVCRT__)&&!defined(__NO_MINGW_LFS) #include<sys/types.h> __CRT_INLINEFILE*__cdeclfopen64(constchar*filename,constchar*mode) { returnfopen(filename,mode); } int__cdeclfseeko64(FILE*,off64_t,int); #ifdef__USE_MINGW_FSEEK int__cdecl__mingw_fseeko64(FILE*,off64_t,int); #definefseeko64(fp,offset,whence)__mingw_fseeko64(fp,offset,whence) #endif __CRT_INLINEoff64_t__cdeclftello64(FILE*stream) { fpos_tpos; if(fgetpos(stream,&pos)) return-1LL; else return((off64_t)pos); } #endif/*__NO_MINGW_LFS*/ #endif/*Not__STRICT_ANSI__*/ /*Wideversions*/ #ifndef_WSTDIO_DEFINED /*alsoinwchar.h-keepinsync*/ _CRTIMPint__cdeclfwprintf(FILE*,constwchar_t*,...); _CRTIMPint__cdeclwprintf(constwchar_t*,...); _CRTIMPint__cdeclswprintf(wchar_t*,constwchar_t*,...); _CRTIMPint__cdecl_snwprintf(wchar_t*,size_t,constwchar_t*,...); _CRTIMPint__cdeclvfwprintf(FILE*,constwchar_t*,__VALIST); _CRTIMPint__cdeclvwprintf(constwchar_t*,__VALIST); _CRTIMPint__cdeclvswprintf(wchar_t*,constwchar_t*,__VALIST); _CRTIMPint__cdecl_vsnwprintf(wchar_t*,size_t,constwchar_t*,__VALIST); _CRTIMPint__cdeclfwscanf(FILE*,constwchar_t*,...); _CRTIMPint__cdeclwscanf(constwchar_t*,...); _CRTIMPint__cdeclswscanf(constwchar_t*,constwchar_t*,...); _CRTIMPwint_t__cdeclfgetwc(FILE*); _CRTIMPwint_t__cdeclfputwc(wchar_t,FILE*); _CRTIMPwint_t__cdeclungetwc(wchar_t,FILE*); #ifdef__MSVCRT__ _CRTIMPwchar_t*__cdeclfgetws(wchar_t*,int,FILE*); _CRTIMPint__cdeclfputws(constwchar_t*,FILE*); _CRTIMPwint_t__cdeclgetwc(FILE*); _CRTIMPwint_t__cdeclgetwchar(void); _CRTIMPwchar_t*__cdecl_getws(wchar_t*); _CRTIMPwint_t__cdeclputwc(wint_t,FILE*); _CRTIMPint__cdecl_putws(constwchar_t*); _CRTIMPwint_t__cdeclputwchar(wint_t); _CRTIMPFILE*__cdecl_wfdopen(int,wchar_t*); _CRTIMPFILE*__cdecl_wfopen(constwchar_t*,constwchar_t*); _CRTIMPFILE*__cdecl_wfreopen(constwchar_t*,constwchar_t*,FILE*); _CRTIMPFILE*__cdecl_wfsopen(constwchar_t*,constwchar_t*,int); _CRTIMPwchar_t*__cdecl_wtmpnam(wchar_t*); _CRTIMPwchar_t*__cdecl_wtempnam(constwchar_t*,constwchar_t*); _CRTIMPint__cdecl_wrename(constwchar_t*,constwchar_t*); _CRTIMPint__cdecl_wremove(constwchar_t*); _CRTIMPvoid__cdecl_wperror(constwchar_t*); _CRTIMPFILE*__cdecl_wpopen(constwchar_t*,constwchar_t*); #endif/*__MSVCRT__*/ #ifndef__NO_ISOCEXT/*externsinlibmingwex.a*/ int__cdeclsnwprintf(wchar_t*s,size_tn,constwchar_t*format,...); __CRT_INLINEint__cdecl vsnwprintf(wchar_t*s,size_tn,constwchar_t*format,__VALISTarg) {return_vsnwprintf(s,n,format,arg);} int__cdeclvwscanf(constwchar_t*__restrict__,__VALIST); int__cdeclvfwscanf(FILE*__restrict__, constwchar_t*__restrict__,__VALIST); int__cdeclvswscanf(constwchar_t*__restrict__, constwchar_t*__restrict__,__VALIST); #endif #define_WSTDIO_DEFINED #endif/*_WSTDIO_DEFINED*/ #ifndef__STRICT_ANSI__ #ifdef__MSVCRT__ #ifndefNO_OLDNAMES _CRTIMPFILE*__cdeclwpopen(constwchar_t*,constwchar_t*); #endif/*notNO_OLDNAMES*/ #endif/*MSVCRTruntime*/ /* *OtherNonANSIwidefunctions */ _CRTIMPwint_t__cdecl_fgetwchar(void); _CRTIMPwint_t__cdecl_fputwchar(wint_t); _CRTIMPint__cdecl_getw(FILE*); _CRTIMPint__cdecl_putw(int,FILE*); #ifndef_NO_OLDNAMES _CRTIMPwint_t__cdeclfgetwchar(void); _CRTIMPwint_t__cdeclfputwchar(wint_t); _CRTIMPint__cdeclgetw(FILE*); _CRTIMPint__cdeclputw(int,FILE*); #endif/*Not_NO_OLDNAMES*/ #endif/*__STRICT_ANSI*/ #ifdef__cplusplus } #endif #endif/*NotRC_INVOKED*/ #endif/*_STDIO_H_*/ stdio.h所包含的函数： 文件访问 fopen freopen fflush fclose 二进制输入/输出 fread fwrite 非格式化输入/输出 fgetc/getc fputc/putc ungetc fgets fputs 格式化输入/输出 scanf/fscanf/sscanf printf/fprintf/sprintf perror 文件定位 ftell fseek fgetpos fsetpos rewind 错误处理 feof ferror 文件操作 remove rename tmpfile