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Dokumen ini menggunakan Manual laman web PHP Cina Lepaskan
在頭文件<stdio.h>中定義 | ||
---|---|---|
(1) | ||
FILE * fopen(const char * filename,const char * mode); | (直到C99) | |
FILE * fopen(const char *限制文件名,const char *限制模式); | (自C99以來(lái)) | |
errno_t fopen_s(FILE * restrict *限制streamptr,const char *限制文件名,const char *限制模式); | (2) | (自C11以來(lái)) |
1)打開由該文件指示的文件filename
并返回指向與該文件關(guān)聯(lián)的文件流的指針。mode
用于確定文件訪問(wèn)模式。
2)與(1)相同,除了寫入指向文件流的指針streamptr
以及在運(yùn)行時(shí)檢測(cè)到以下錯(cuò)誤并調(diào)用當(dāng)前安裝的約束處理函數(shù):
streamptr
是一個(gè)空指針
filename
是一個(gè)空指針
mode
是一個(gè)空指針
作為所有邊界檢查函數(shù),fopen_s
只有在被__STDC_LIB_EXT1__
實(shí)現(xiàn)定義__STDC_WANT_LIB_EXT1__
并且1
在包含之前用戶定義為整數(shù)常量時(shí)才能保證可用<stdio.h>
。
文件名 | - | 將文件流關(guān)聯(lián)到的文件名 | |||||||||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
模式 | - | null-terminated character string determining file access mode File access mode string Meaning Explanation Action if file already exists Action if file does not exist "r" read Open a file for reading read from start failure to open "w" write Create a file for writing destroy contents create new "a" append Append to a file write to end create new "r+" read extended Open a file for read/write read from start error "w+" write extended Create a file for read/write destroy contents create new "a+" append extended Open a file for read/write write to end create new File access mode flag "b" can optionally be specified to open a file in binary mode. This flag has effect only on Windows systems. On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator. When a file is opened with update mode ('+' as the second or third character in the above list of mode argument values), both input and output may be performed on the associated stream. However, output shall not be directly followed by input without an intervening call to the fflush function or to a file positioning function (fseek, fsetpos, or rewind), and input shall not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end- of-file. Opening (or creating) a text file with update mode may instead open (or create) a binary stream in some implementations. File access mode flag "x" can optionally be appended to "w" or "w+" specifiers. This flag forces the function to fail if the file exists, instead of overwriting it. (C11) When using fopen_s or freopen_s, file access permissions for any file created with "w" or "a" prevents other users from accessing it. File access mode flag "u" can optionally be prepended to any specifier that begins with "w" or "a", to enable the default fopen permissions. (C11) | File access mode string | Meaning | Explanation | Action if file already exists | Action if file does not exist | "r" | read | Open a file for reading | read from start | failure to open | "w" | write | Create a file for writing | destroy contents | create new | "a" | append | Append to a file | write to end | create new | "r+" | read extended | Open a file for read/write | read from start | error | "w+" | write extended | Create a file for read/write | destroy contents | create new | "a+" | append extended | Open a file for read/write | write to end | create new | File access mode flag "b" can optionally be specified to open a file in binary mode. This flag has effect only on Windows systems. On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator. | When a file is opened with update mode ('+' as the second or third character in the above list of mode argument values), both input and output may be performed on the associated stream. However, output shall not be directly followed by input without an intervening call to the fflush function or to a file positioning function (fseek, fsetpos, or rewind), and input shall not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end- of-file. Opening (or creating) a text file with update mode may instead open (or create) a binary stream in some implementations. | File access mode flag "x" can optionally be appended to "w" or "w+" specifiers. This flag forces the function to fail if the file exists, instead of overwriting it. (C11) | 當(dāng)使用fopen_s或freopen_s時(shí),用“w”或“a”創(chuàng)建的任何文件的文件訪問(wèn)權(quán)限會(huì)阻止其他用戶訪問(wèn)它。文件訪問(wèn)模式標(biāo)志“u”可以有選擇地添加到以“w”或“a”開頭的任何說(shuō)明符中,以啟用默認(rèn)的fopen權(quán)限。(C11) |
文件訪問(wèn)模式字符串 | 含義 | 說(shuō)明 | 行動(dòng)如果文件已經(jīng)存在 | 如果文件不存在,則采取行動(dòng) | |||||||||||||||||||||||||||||||||||||
“R” | 讀 | 打開一個(gè)文件以供閱讀 | 從開始閱讀 | 未能打開 | |||||||||||||||||||||||||||||||||||||
“W” | 寫 | 創(chuàng)建一個(gè)文件寫入 | 破壞內(nèi)容 | 創(chuàng)建新的 | |||||||||||||||||||||||||||||||||||||
“一個(gè)” | 附加 | 附加到文件 | 寫入結(jié)束 | 創(chuàng)建新的 | |||||||||||||||||||||||||||||||||||||
“R +” | 閱讀擴(kuò)展 | 打開文件進(jìn)行讀取/寫入 | 從開始閱讀 | 錯(cuò)誤 | |||||||||||||||||||||||||||||||||||||
“W +” | 寫入擴(kuò)展 | 創(chuàng)建一個(gè)用于讀/寫的文件 | 破壞內(nèi)容 | 創(chuàng)建新的 | |||||||||||||||||||||||||||||||||||||
“A +” | 追加擴(kuò)展 | 打開文件進(jìn)行讀取/寫入 | 寫入結(jié)束 | 創(chuàng)建新的 |
| 可以選擇指定文件訪問(wèn)模式標(biāo)志“b”以二進(jìn)制模式打開文件。該標(biāo)志只對(duì)Windows系統(tǒng)有效。在附加文件訪問(wèn)模式下,無(wú)論文件位置指示符的當(dāng)前位置如何,數(shù)據(jù)都會(huì)寫入文件末尾。|
| 當(dāng)以更新模式('+'作為上述模式參數(shù)值列表中的第二個(gè)或第三個(gè)字符)打開文件時(shí),可以在關(guān)聯(lián)的流上執(zhí)行輸入和輸出。然而,輸出不應(yīng)直接跟隨輸入而沒(méi)有插入調(diào)用fflush函數(shù)或文件定位函數(shù)(fseek,fsetpos,或倒帶),并且輸入不應(yīng)直接跟隨輸出而沒(méi)有中間呼叫到一個(gè)文件中的定位函數(shù),除非輸入操作遇到文件結(jié)束。在某些實(shí)現(xiàn)中打開(或創(chuàng)建)具有更新模式的文本文件可能會(huì)打開(或創(chuàng)建)二進(jìn)制流。|
| 文件訪問(wèn)模式標(biāo)志“x”可以選擇性地附加到“w”或“w +”說(shuō)明符。如果文件存在,該標(biāo)志強(qiáng)制該功能失敗,而不是覆蓋它。(C11)|
| 當(dāng)使用fopen_s或freopen_s時(shí),用“w”或“a”創(chuàng)建的任何文件的文件訪問(wèn)權(quán)限會(huì)阻止其他用戶訪問(wèn)它。文件訪問(wèn)模式標(biāo)志“u”可以有選擇地添加到以“w”或“a”開頭的任何說(shuō)明符中,以啟用默認(rèn)的fopen權(quán)限。(C11)|
| streamptr | - | 指向函數(shù)存儲(chǔ)結(jié)果的指針(out-parameter)|的指針
1)如果成功,返回一個(gè)指向新文件流的指針。除非filename
指向交互式設(shè)備,否則該流完全緩沖。出錯(cuò)時(shí),返回一個(gè)null pointer
。POSIX需要的是errno
在這種情況下設(shè)置。
2)如果成功,則返回零,并寫入指向新文件流的指針*streamptr
。出錯(cuò)時(shí),返回一個(gè)非零的錯(cuò)誤代碼并將空指針寫入*streamptr
(除非streamptr
是空指針本身)。
格式filename
是實(shí)現(xiàn)定義的,并不一定是指文件(例如它可能是控制臺(tái)或通過(guò)文件系統(tǒng)API可訪問(wèn)的其他設(shè)備)。在支持它們的平臺(tái)上,filename
可能包括絕對(duì)或相對(duì)的文件系統(tǒng)路徑。
#include <stdio.h>#include <stdlib.h> int main(void){ FILE* fp = fopen("test.txt", "r"); if(!fp) { perror("File opening failed"); return EXIT_FAILURE; } int c; // note: int, not char, required to handle EOF while ((c = fgetc(fp)) != EOF) { // standard C I/O file reading loop putchar(c); } if (ferror(fp)) puts("I/O error when reading"); else if (feof(fp)) puts("End of file reached successfully"); fclose(fp);}
C11標(biāo)準(zhǔn)(ISO / IEC 9899:2011):
7.21.5.3 fopen函數(shù)(p:305-306)
K.3.5.2.1 fopen_s函數(shù)(p:588-590)
C99標(biāo)準(zhǔn)(ISO / IEC 9899:1999):
7.19.5.3 fopen函數(shù)(p:271-272)
C89 / C90標(biāo)準(zhǔn)(ISO / IEC 9899:1990):
4.9.5.3 fopen函數(shù)