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Fastest way to read a file into a char*
- Thread starter jsitke
- Start date
- Thread starter
- #2
Cagliostro
Programmer
try to use ifstream::rdbuf. John Fill
ivfmd@mail.md
ivfmd@mail.md
- Thread starter
- #4
Why are the buffers only a sizeof 4 after the code is excuted? I need to fill the buffer completely.
Code:
long lSize;
char * buffer;
lSize = 10504120
ifstream in;
in.open (fileName);
filebuf *pbuf;
pbuf=in.rdbuf();
pbuf->sgetn (buffer,lSize);
cout << "Buffer Size:" << sizeof(buffer) << endl;
cout << "PBuffer Size:" << sizeof(pbuf) << endl;Cagliostro
Programmer
you return there size of pointer, not the size of allocated memory it points. John Fill
ivfmd@mail.md
ivfmd@mail.md
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- #6
- Thread starter
- #7
I am now trying this code block:
And I get these of compilation errors:
D:\DOCs\inetConsole\inetConsole.cpp(307) : error C2079: 'in' uses undefined class 'basic_ifstream<char,struct std::char_traits<char> >'
D:\DOCs\inetConsole\inetConsole.cpp(307) : error C2440: 'initializing' : cannot convert from 'char *' to 'int'
This conversion requires a reinterpret_cast, a C-style cast or function-style cast
D:\DOCs\inetConsole\inetConsole.cpp(308) : error C2079: 'tmp' uses undefined class 'basic_ostringstream<char,struct std::char_traits<char>,class std::allocator<char> >'
D:\DOCs\inetConsole\inetConsole.cpp(309) : error C2228: left of '.rdbuf' must have class/struct/union type
D:\DOCs\inetConsole\inetConsole.cpp(310) : error C2228: left of '.str' must have class/struct/union type
D:\DOCs\inetConsole\inetConsole.cpp(324) : error C2228: left of '.eof' must have class/struct/union type
Code:
#include <string>
std::ifstream in(fileName);
std::ostringstream tmp;
tmp << in.rdbuf();
std::string str = tmp.str();And I get these of compilation errors:
D:\DOCs\inetConsole\inetConsole.cpp(307) : error C2079: 'in' uses undefined class 'basic_ifstream<char,struct std::char_traits<char> >'
D:\DOCs\inetConsole\inetConsole.cpp(307) : error C2440: 'initializing' : cannot convert from 'char *' to 'int'
This conversion requires a reinterpret_cast, a C-style cast or function-style cast
D:\DOCs\inetConsole\inetConsole.cpp(308) : error C2079: 'tmp' uses undefined class 'basic_ostringstream<char,struct std::char_traits<char>,class std::allocator<char> >'
D:\DOCs\inetConsole\inetConsole.cpp(309) : error C2228: left of '.rdbuf' must have class/struct/union type
D:\DOCs\inetConsole\inetConsole.cpp(310) : error C2228: left of '.str' must have class/struct/union type
D:\DOCs\inetConsole\inetConsole.cpp(324) : error C2228: left of '.eof' must have class/struct/union type
maybe change the size of rdbuf like this example:
const int BuffSize = 4096; // or whatever you want
char FileBuffer[BuffSize];
in.rdbuf()->pubsetbuf(FileBuffer, BuffSize);
// returns a streambuf
However, I am not sure how the destructor for your fstream deals with your rdbuf, you might have to save the old buffer as a streambuf and restore it before the fstream goes out of scope.
const int BuffSize = 4096; // or whatever you want
char FileBuffer[BuffSize];
in.rdbuf()->pubsetbuf(FileBuffer, BuffSize);
// returns a streambuf
However, I am not sure how the destructor for your fstream deals with your rdbuf, you might have to save the old buffer as a streambuf and restore it before the fstream goes out of scope.
- Thread starter
- #9
I need to contain the entire file stream in the buffer, therefore the buffer should be the same size as the file. I am running the code below, but it seems to hang. However if I output to a file
it does not hang...
Code:
ofstream out ("test.txt",ofstream::binary)
Code:
{
char *buff;
long size;
ifstream infile (fileName);
infile.seekg(0,ifstream::end);
size=infile.tellg();
infile.seekg(0);
buff = new char [size];
infile.read(buff,lSize);
std::ostringstream out;
out.write (buff,lSize);
std::string mystr = out.str();
}Segfault7375
Programmer
Code:
#include <string>
std::ifstream in(fileName);
std::ostringstream tmp;
tmp << in.rdbuf();
std::string str = tmp.str();
And I get these of compilation errors:
D:\DOCs\inetConsole\inetConsole.cpp(307) : error C2079: 'in' uses undefined class 'basic_ifstream<char,struct std::char_traits<char> >'
D:\DOCs\inetConsole\inetConsole.cpp(307) : error C2440: 'initializing' : cannot convert from 'char *' to 'int'
This conversion requires a reinterpret_cast, a C-style cast or function-style cast
D:\DOCs\inetConsole\inetConsole.cpp(308) : error C2079: 'tmp' uses undefined class 'basic_ostringstream<char,struct std::char_traits<char>,class std::allocator<char> >'
D:\DOCs\inetConsole\inetConsole.cpp(309) : error C2228: left of '.rdbuf' must have class/struct/union type
D:\DOCs\inetConsole\inetConsole.cpp(310) : error C2228: left of '.str' must have class/struct/union type
D:\DOCs\inetConsole\inetConsole.cpp(324) : error C2228: left of '.eof' must have class/struct/union typeDon't forget to
Code:
#include <fstream.h>
Cagliostro
Programmer
#include<strstream> John Fill
ivfmd@mail.md
ivfmd@mail.md
Use memory-mapped files. The operating system (Windows NT 3.1 or later, Windows 95 or later) handles the paging for you. It's pretty sweet.
Open a file for reading as usual with CreateFile(). Then call:
[tt]
hMapFile = CreateFileMapping(hFile, NULL, PAGE_READWRITE, 0, 0, "MyFileMappingObject"
;[/tt]
Then call:
[tt]
LPVOID lpMapAddress;
lpMapAddress = MapViewOfFile(hMapFile, FILE_MAP_ALL_ACCESS, 0, 0, 0);
[/tt]
You would then access the file through the lpMapAddress pointer. Be sure to call UnMapViewOfFile() and CloseHandle() when you're done.
Chip H.
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