C++对txt文件的读写问题？

2013-07-03 10:57:10 214 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

c++ 开发中读写yaml配置文件 4、创建自己测试用的文件夹，将yaml-cpp目录下面的include 目录拷贝到测试目录下，将编译后的动态库也拷贝到测试目录下，同事目录下在编写三个文件，分别为CMakeLists.txt、config.yaml、main.cpp。1、yaml-cpp 是一个开源库，地址在 github 上，https://github.com/jbeder/yaml-cpp。2、进入到yaml-cpp目录，新建一个build目录。获取yaml-cpp源码。在ubuntu中可以输入。阅读详情

可以打开一个text.txt文件，同时对它进行即读又写吗？比方说写第十个数据后读二个，或者第三个数据

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C++读写txt文件本文主要介绍：C++利用ifstream和ofstream函数读写txt文件，包含矩阵以及字符串的读写。说明：需要添加的头文件有： #include #include 阅读详情

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我看你有戏 2013-07-04

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引用楼主 u011288669 的回复:

可以打开一个text.txt文件，同时对它进行即读又写吗？比方说写第十个数据后读二个，或者第三个数据

楼主是想实现多线程操作这个text.txt吗，读写同时进行？不要这么搞，windows操作系统会给你排队的

橡木疙瘩 2013-07-03

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可以，用fstream即可。不过读写指针是分开的。

qzf362269994 2013-07-03

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每次操作前先进行定标下，

水平不流 2013-07-03

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最好还是不要这么做.

赵4老师 2013-07-03

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fopen, _wfopen Open a file. FILE *fopen( const char *filename, const char *mode ); FILE *_wfopen( const wchar_t *filename, const wchar_t *mode ); Function Required Header Compatibility fopen <stdio.h> ANSI, Win 95, Win NT _wfopen <stdio.h> or <wchar.h> Win NT For additional compatibility information, see Compatibility in the Introduction. Libraries LIBC.LIB Single thread static library, retail version LIBCMT.LIB Multithread static library, retail version MSVCRT.LIB Import library for MSVCRT.DLL, retail version The c, n, and t mode options are Microsoft extensions for fopen and _fdopen and should not be used where ANSI portability is desired. Return Value Each of these functions returns a pointer to the open file. A null pointer value indicates an error. Parameters filename Filename mode Type of access permitted Remarks The fopen function opens the file specified by filename. _wfopen is a wide-character version of fopen; the arguments to _wfopen are wide-character strings. _wfopen and fopen behave identically otherwise. Generic-Text Routine Mappings TCHAR.H Routine _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined _tfopen fopen fopen _wfopen The character string mode specifies the type of access requested for the file, as follows: "r" Opens for reading. If the file does not exist or cannot be found, the fopen call fails. "w" Opens an empty file for writing. If the given file exists, its contents are destroyed. "a" Opens for writing at the end of the file (appending) without removing the EOF marker before writing new data to the file; creates the file first if it doesn’t exist. "r+" Opens for both reading and writing. (The file must exist.) "w+" Opens an empty file for both reading and writing. If the given file exists, its contents are destroyed. "a+" Opens for reading and appending; the appending operation includes the removal of the EOF marker before new data is written to the file and the EOF marker is restored after writing is complete; creates the file first if it doesn’t exist. When a file is opened with the "a" or "a+" access type, all write operations occur at the end of the file. The file pointer can be repositioned using fseek or rewind, but is always moved back to the end of the file before any write operation is carried out. Thus, existing data cannot be overwritten. The "a" mode does not remove the EOF marker before appending to the file. After appending has occurred, the MS-DOS TYPE command only shows data up to the original EOF marker and not any data appended to the file. The "a+" mode does remove the EOF marker before appending to the file. After appending, the MS-DOS TYPE command shows all data in the file. The "a+" mode is required for appending to a stream file that is terminated with the CTRL+Z EOF marker. When the "r+", "w+", or "a+" access type is specified, both reading and writing are allowed (the file is said to be open for “update”). However, when you switch between reading and writing, there must be an intervening fflush, fsetpos, fseek, or rewind operation. The current position can be specified for the fsetpos or fseek operation, if desired. In addition to the above values, the following characters can be included in mode to specify the translation mode for newline characters: t Open in text (translated) mode. In this mode, CTRL+Z is interpreted as an end-of-file character on input. In files opened for reading/writing with "a+", fopen checks for a CTRL+Z at the end of the file and removes it, if possible. This is done because using fseek and ftell to move within a file that ends with a CTRL+Z, may cause fseek to behave improperly near the end of the file. Also, in text mode, carriage return–linefeed combinations are translated into single linefeeds on input, and linefeed characters are translated to carriage return–linefeed combinations on output. When a Unicode stream-I/O function operates in text mode (the default), the source or destination stream is assumed to be a sequence of multibyte characters. Therefore, the Unicode stream-input functions convert multibyte characters to wide characters (as if by a call to the mbtowc function). For the same reason, the Unicode stream-output functions convert wide characters to multibyte characters (as if by a call to the wctomb function). b Open in binary (untranslated) mode; translations involving carriage-return and linefeed characters are suppressed. If t or b is not given in mode, the default translation mode is defined by the global variable _fmode. If t or b is prefixed to the argument, the function fails and returns NULL. For more information about using text and binary modes in Unicode and multibyte stream-I/O, see Text and Binary Mode File I/O and Unicode Stream I/O in Text and Binary Modes. c Enable the commit flag for the associated filename so that the contents of the file buffer are written directly to disk if either fflush or _flushall is called. n Reset the commit flag for the associated filename to “no-commit.” This is the default. It also overrides the global commit flag if you link your program with COMMODE.OBJ. The global commit flag default is “no-commit” unless you explicitly link your program with COMMODE.OBJ. Valid characters for the mode string used in fopen and _fdopen correspond to oflag arguments used in _open and _sopen, as follows. Characters in mode String Equivalent oflag Value for _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: This program opens files named "data" * and "data2".It uses fclose to close "data" and * _fcloseall to close all remaining files. */ #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" ); else printf( "The file 'data' was opened\n" ); /* Open for write */ if( (stream2 = fopen( "data2", "w+" )) == NULL ) printf( "The file 'data2' was not opened\n" ); else printf( "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 ); } Output The file 'data' was opened The file 'data2' was opened Number of files closed by _fcloseall: 1 Stream I/O Routines See Also fclose, _fdopen, ferror, _fileno, freopen, _open, _setmode

rocktyt 2013-07-03

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fstream不好用啊，我从来就没成功同时读写过，很容易乱宁可全部读进内存，操作完成后全部写到文件

ztenv 版主 2013-07-03

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两种方式：一种是使用FILE；使用fopen等函数；另一种是使用fstream；流

xiaohuh421 2013-07-03

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详见fopen函数的说明, 通过不同的打开标记, 可以有你想要的功能.

C++对txt文件的读写问题？

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