C++ file stream open mode vs C file stream open mode in Visual C++ 2013

最新推荐文章于 2024-09-29 17:05:39 发布

原创最新推荐文章于 2024-09-29 17:05:39 发布 · 1.2k 阅读

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本文探讨了C++中文件流(filestream)的有效打开模式，包括各种模式的组合及其对应的fopen字符串表示形式。通过静态数组定义了有效的模式组合，并解释了如何根据这些模式进行文件的读写操作。

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//C++ file stream valid stream open mode

	ios_base::openmode mode;

	{
	static const int valid[] =
		{	// valid combinations of open flags
		ios_base::in,
		ios_base::out,
		ios_base::out | ios_base::trunc,
		ios_base::out | ios_base::app,
		ios_base::in | ios_base::binary,
		ios_base::out | ios_base::binary,
		ios_base::out | ios_base::trunc | ios_base::binary,
		ios_base::out | ios_base::app | ios_base::binary,
		ios_base::in | ios_base::out,
		ios_base::in | ios_base::out | ios_base::trunc,
		ios_base::in | ios_base::out | ios_base::app,
		ios_base::in | ios_base::out | ios_base::binary,
		ios_base::in | ios_base::out | ios_base::trunc
			| ios_base::binary,
		ios_base::in | ios_base::out | ios_base::app
			| ios_base::binary,
		0};

	FILE *fp = 0;
	int n;
	ios_base::openmode atendflag = mode & ios_base::ate;
	ios_base::openmode norepflag = mode & ios_base::_Noreplace;

	if (mode & ios_base::_Nocreate)
		mode |= ios_base::in;	// file must exist
	if (mode & ios_base::app)
		mode |= ios_base::out;	// extension -- app implies out

	mode &= ~(ios_base::ate | ios_base::_Nocreate | ios_base::_Noreplace);
	for (n = 0; valid[n] != 0 && valid[n] != mode; ++n)
		;	// look for a valid mode

//C file stream valid open mode

	static const char * const mods[] =
		{	// fopen mode strings corresponding to valid[i]
		"r", "w", "w", "a",
		"rb", "wb", "wb", "ab",
		"r+", "w+", "a+",
		"r+b", "w+b", "a+b",
		0};