From k.zhong at erasmusmc.nl  Wed Sep 23 15:46:14 2015
From: k.zhong at erasmusmc.nl (K. Zhong)
Date: Wed, 23 Sep 2015 13:46:14 +0000
Subject: [GenABEL-dev] truncate end of file with Rcpp
Message-ID: <D22879C6.1FD0%k.zhong@erasmusmc.nl>

Dear list,

Since the `truncate` function is not working properly on Windows (see ?truncate), and CollapsABEL depends on such a function, I tried to implement it with c++ (to be integrated into R with Rcpp):



#include <SDKDDKVer.h>

#include <windows.h>

#include <tlhelp32.h>

#include <tchar.h>

#include <stdio.h>

#include <iostream>

#include <string>

#include <sstream>

#include <Rcpp.h>


using namespace Rcpp;


typedef const char* LPCTSTR;

typedef const void* LPCVOID;

typedef unsigned long DWORD;


// [[Rcpp::export]]

void append(LPCTSTR filename, LPCVOID buf, DWORD writeSize) {

LARGE_INTEGER size;

size.QuadPart = 0;

HANDLE fh = CreateFile(filename, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

if (fh == INVALID_HANDLE_VALUE) {

std::ostringstream error;

error << "Failed to created file: " << filename << "\nError: " << GetLastError();

throw error.str();

}

GetFileSizeEx(fh, &size);

SetFilePointerEx(fh, size, NULL, FILE_BEGIN);

if (WriteFile(fh, buf, writeSize, NULL, NULL) == 0) {

std::ostringstream error;

error << "Failed to write file: " << filename << "\nError: " << GetLastError();

throw error.str();

}

CloseHandle(fh);

}


// [[Rcpp::export]]

std::string readTail(LPCTSTR filename,  DWORD readSize) {

char *buf = "";

LARGE_INTEGER size;

size.QuadPart = 0;

HANDLE fh = CreateFile(filename, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

if (fh == INVALID_HANDLE_VALUE) {

std::ostringstream error;

error << "Failed to created file: " << filename << "\nError: " << GetLastError();

throw error.str();

}

GetFileSizeEx(fh, &size);

size.QuadPart -= readSize;

SetFilePointerEx(fh, size, NULL, FILE_BEGIN);

if (ReadFile(fh, buf, readSize, NULL, NULL) == 0) {

std::ostringstream error;

error << "Failed to read file: " << filename << "\nError: " << GetLastError();

throw error.str();

}

CloseHandle(fh);

std::string s(buf);

}


// [[Rcpp::export]]

std::string hello(std::string name) {

std::ostringstream s;

s << "Hello, " << name << "\n";

return s.str();

}


// [[Rcpp::export]]

void truncateTail(LPCTSTR filename, long truncateSize) {

LARGE_INTEGER size;

size.QuadPart = 0;

HANDLE fh = CreateFile(filename, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

if (fh == INVALID_HANDLE_VALUE) {

std::ostringstream error;

error << "Failed to created file: " << filename << "\nError: " << GetLastError();

throw error.str();

}

GetFileSizeEx(fh, &size);

size.QuadPart -= truncateSize;

SetFilePointerEx(fh, size, NULL, FILE_BEGIN);

if (SetEndOfFile(fh) == 0) {

std::ostringstream error;

error << "Failed to set end of file: " << filename << "\nError: " << GetLastError();

throw error.str();

}

CloseHandle(fh);

}


A quick import with `sourceCpp` seems to compile this just fine, but when I call `truncateTail("C:/kaiyin/kybig.out", 3L)`, I get this:



Error in truncateTail("C:/kaiyin/kybig.out", 3L) :

  c++ exception (unknown reason)


Any suggestions?


Best regards,

Kaiyin ZHONG
------------------
FMB, Erasmus MC
http://kspace.co.vu
k.zhong at erasmusmc.nl<mailto:k.zhong at erasmusmc.nl>
kindlychung at gmail.com<mailto:kindlychung at gmail.com>


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