I'm currently working with a function call that uses FILE *, but I need to get data from the FILE * into a buffer without letting the data touch the HDD. My first idea was to convert FILE * to a CMemFile, but I cannot find a way to do this. Any ideas?
Using MFC...
This question comes up from using the JPEG library by IJG whose homepage can be found here: http://www.ijg.org/
You can use setvbuf to make a FILE pointer use a predefined (and filled) buffer.
Related
I currently have some code reading files which are not compressed, it uses the following approach to read a file in C++
FILE* id = fopen("myfile.dat", "r");
after obtaining id, different parts of the code access the file using fread, fseek, etc.
I would like to adapt my code so as to open a gzip version of the file, e.g. "myfile.dat.gz" without needing to change too much.
Ideally I would implement a wrapper to fopen, call it fopen2, which can read both myfile.dat and myfile.dat.gz, i.e. it should return a pointer to a FILE object, so that the remaining of the code does not need to be changed.
Any suggestions?
Thank you.
PS: it would be fine to decompress the whole file in memory, if this approach provides a solution
zlib provides analogs of fopen(), fread(), etc. called gzopen(), gzread(), etc. for reading and writing gzip files. If the file is not gzip-compressed, it will be read just as the f functions would. So you would only need to change the function names and link in zlib.
Hi I have an image in my memory and I want to sent it through an external FTP library.
This FTP library accepts only and only standard C FILE and the sample codes provided by this library reads data only from hard disk. In my application I don't want to store my images in the hard disk and then read them using FILE variable, instead I want to do the conversion in my memory so it's faster and more professional.
My image is in the form of uchar * but I can change it to std::String or QByteArray or any other type of string. Now I want to know how can I have a file which is filled by my image data so I will get rid of storing it into the hard disk and read it again.
My pseudo code:
uchar * image = readImage();
FILE * New_Image = String2FileConverter(image); //I need this function
FTP_Upload(New_Image);
On Posix systems, you can use fmemopen to create a memory-backed file handle.
Is there any way to create a data stream that is located at the beginning of a memory mapped file in Qt?
Once i use QFile::map method, i get a uchar*. So is there any way to initialize a data stream with it? Thanks in advance!
I've not tried it but there's a QDataStream::readRawData() function that accepts a char * and a length which you should be able to pipe that uchar * into. That'll give you your stream.
I am trying to load a bitmap from an archive. The bitmap class I have takes a character pointer to a filename and then loads it if it is in the same directory. The bitmap loading class is well tested and I don't want to mess with it too much. Problem is it uses a file pointer to load and do all of its file manipulation. Is there any way to emulate a file pointer and actually have it read from a chunk in memory instead?
Sorry if this is a bizarre question.
Refactor it and create functions that takes the exact same parameters as before : If you used fopen, fread and fseek that read from disk, create mopen, mread and mseek that read file from memory. You'll only have to fix the name of the functions.
It should be easy without risk and code won't look like an dirty hack in the end.
You can also use a pipe. A pipe is a piece of memory where you can read and write using file primitives. Which is basically what you want
(Assuming POSIX Operating system)
create a pipe:
int p[2];
pipe(p);
use fdopen() to turn the pipe file descriptor into a FILE*
FILE *emulated_file = fdopen(p[0], "r");
then write whatever you want to the write end of the pipe :
write(p[1], 17 ,"whatevereyouwant");
Now :
buf[32];
fread(&buf,1,32, emulated_file);
cout<<buf<<endl;
willl output "whateveryouwant".
Check out John Ratcliff's File Interface replacement for standard file I/O. It supports the feature you need.
You'll still need to refactor the bitmap loading code to use the new interface. However, this interface supports loading from file on disk, or memory chunk in memory (as well as writing to file on disk, or to expandable memory chunks).
I'm trying to connect the output of popen, a file pointer, to the input of TinyXML.
According to the main page, the best way to do it is using the parse method:
C style input:
* based on FILE*
* the Parse() and LoadFile() methods
I believe I need to use the TIXML_USE_STL to get to this. How do I go about finding examples and import it?
A reply since deleted pointed me in the right direction on the docs
http://www.grinninglizard.com/tinyxmldocs/index.html
Thanks.
Now, i just need to figure out how to link and import it.
I'm not hugely familiar with TinyXML, but does LoadFile() not work in its overloaded version which takes a FILE *?
http://www.grinninglizard.com/tinyxmldocs/classTiXmlDocument.html#a12
EDIT: Ah, the problem is that TinyXML doesn't support reading from a stream (see the link above). Your only choice then is to read the stream manually into a buffer and pass it to TinyXML's Parse().
You can read the file data into some buffer (say SomeCharBuffer), append null terminator to it and do
TiXmlDocument doc;
doc.Parse(SomeCharBuffer);