scope exit lambda

scope_exit_lambda.cpp

namespace cxxdetail
{
	template <typename FuncType>
	class InnerScopeExit
	{
	public:
		InnerScopeExit(const FuncType _func) :func(_func){}
		~InnerScopeExit(){ if (!dismissed){ func(); } }
	private:
		FuncType func;
		bool dismissed = false;
	};
	template <typename F>
	InnerScopeExit<F> MakeScopeExit(F f) {
		return InnerScopeExit<F>(f);
	};
}

#define DO_STRING_JOIN(arg1, arg2) arg1 ## arg2
#define STRING_JOIN(arg1, arg2) DO_STRING_JOIN(arg1, arg2)
#define SCOPEEXIT(code) auto STRING_JOIN(scope_exit_object_, __LINE__) = cxxdetail::MakeScopeExit([&](){code;});

void copy(const char* src_file_path,const char* dst_file_path)
{
	FILE* fp_src = fopen(src_file_path, "rb");
	SCOPEEXIT(if (fp_src){ fclose(fp_src); });
	if (!fp_src)
	{
		return;
	}

	//get file length
	fseek(fp_src, 0, SEEK_SET);
	fseek(fp_src, 0, SEEK_END);
	const long longBytes = ftell(fp_src);
	if (longBytes <= 0)
	{
		return;
	}
	fseek(fp_src, 0, SEEK_SET);
	
	//do copy
	FILE* fp_dst = fopen(dst_file_path, "wb");
	SCOPEEXIT(if (fp_dst){ fclose(fp_dst); });
	if (!fp_dst)
	{
		return;
	}	
	const int buffer_len = 4*1024;
	char buffer[buffer_len];
	int read_len = 0;
	while ((read_len = fread(buffer, 1, buffer_len, fp_src)) > 0)
	{
		fwrite(buffer, 1, read_len, fp_dst);
	}
}