There's some path as QString:
QString path = "C:/bla/blah/x/y/file.xls";
I thought that maybe getting last offset of / would be a good start. I could then use right method (no pun intended) to get everything after that character:
path = path.right(path.lastIndexOf("/"));
or in a more compatible way:
path = path.right(std::max(path.lastIndexOf("\\"), path.lastIndexOf("/")));
Those both have the same bad result:
ah/x/y/file.xls
What's wrong here? Obviously the path is getting cut too soon, but it's even weirder it's not cut at any of / at all.
The QString method you want is mid, not right (right counts from the end of the string):
path = path.mid(path.lastIndexOf("/"));
mid has a second parameter, but when it's omitted you get the rightmost part of the string.
And for a cleaner / more universal code:
QFileInfo fi("C:/bla/blah/x/y/file.xls");
QString fileName = fi.fileName();
NB QFileInfo doesn't query the file system when it doesn't have to, and here it doesn't have to because all the infos are in the string.
From QString::right():
"Returns a substring that contains the n rightmost characters of the string."
You're using the index as a count. You'd have to use .size() - .indexOf().
Related
I have user-provided format string (e.g. "%.2f") and a QVariant type that I am attempting to combine to output into a (formatted) string.
I had gone down the path of using QString::asprintf(const char *cformat, ...) to achieve this, where I would supply the appropriate converted data type, like this:
QString result_str = QString::asprintf(disp_fmt.toUtf8(),variant_type.toUInt());
This works fine for the most part, especially when I have a floating point as the input. However, if my format string in this particular integer (.toUInt()) conversion case includes decimal formatting (e.g. "%.2f"), then I get a constant result of "0.00". This caught me by surprise as I expected to instead just get ".00" tacked onto the integer, as I have seen in other languages like Perl.
What am I missing here? Also, I know asprintf() was added fairly recently and the documentation already now advises to use QTextStream or arg() instead. I don't believe this to be an option, however, for me to use this style of format string. Thanks.
The format string is expecting a double, but you're providing an int. It works if you provide an actual double, like this:
QString result_str = QString::asprintf(disp_fmt.toUtf8(),variant_type.toDouble());
Also note, this behavior is identical to how the standard C library functions work (std::sprintf, etc).
I am trying to compare a string (in memory) to the contents of a file to see if they are the same. Boring details on motivation are below the question if anyone cares.
My confusion is that when I hash file contents, I get a different result than when I hash the string.
library(readr)
library(digest)
# write the string to the file
the_string <- "here is some stuff"
the_file <- "fake.txt"
readr::write_lines(the_string, the_file)
# both of these functions (predictably) give the same hash
tools::md5sum(the_file)
# "44b0350ee9f822d10f2f9ca7dbe54398"
digest(file = the_file)
# "44b0350ee9f822d10f2f9ca7dbe54398"
# now read it back to a string and get something different
back_to_a_string <- readr::read_file(the_file)
# "here is some stuff\n"
digest(back_to_a_string)
# "03ed1c8a2b997277100399bef6f88939"
# add a newline because that's what write_lines did
orig_with_newline <- paste0(the_string, "\n")
# "here is some stuff\n"
digest(orig_with_newline)
# "03ed1c8a2b997277100399bef6f88939"
What I want to do is just digest(orig_with_newline) == digest(file = the_file) to see if they're the same (they are) but that returns FALSE because, as shown, the hashes are different.
Obviously I could either read the file back to a string with read_file or write the string to a temp file, but both of those seem a bit silly and hacky. I guess both of those are actually fine solutions, I really just want to understand why this is happening so that I can better understand how the hashing works.
Boring details on motivation
The situation is that I have a function that will write a string to a file, but if the file already exists then it will error unless the user has explicitly passed .overwrite = TRUE. However, if the file exists, I would like to check whether the string about to be written to the file is in fact the same thing that's already in the file. If this is the case, then I will skip the error (and the write). This code could be called in a loop and it will be obnoxious for the user to continually see this error that they are about to overwrite a file with the same thing that's already in it.
Short answer: I think you need to set serialize=FALSE. Supposing that the file doesn't contain the extra newline (see below),
digest(the_string,serialize=FALSE) == digest(file=the_file) ## TRUE
(serialize has no effect on the file= version of the command)
dealing with newlines
If you read ?write_lines, it only says
sep: The line separator ... [information about defaults for different OSes]
To me, this seems ambiguous as to whether the separator will be added after the last line or not. (You don't expect a "comma-separated list" to end with a comma ...)
On the other hand, ?base::writeLines is a little more explicit,
sep: character string. A string to be written to the connection
after each line of text.
If you dig down into the source code of readr you can see that it uses
output << na << sep;
for each line of code, i.e. it's behaving the same way as writeLines.
If you really just want to write the string to the file with no added nonsense, I suggest cat():
identical(the_string, { cat(the_string,file=the_file); readr::read_file(the_file) }) ## TRUE
I have a textfile generated by
find Path -printf '%s\t%p\n' > textfile
When I do
declare -A DICT;
while IFS='\t' read -r SIZE PFAD
do DICT[$SIZE]=$PFAD
done < ../Listen/textfile
the content of DICT surprises me:
print "${(#k)DICT}"
shows, that the keys of DICT are not just the SIZE of the files, but consist of
SIZE\tRoot_of_PFAD/2_letters_of_following_directory.
The values contain the rest of the line = Rest of the path with the filename.
Looks to me as if read separates the lines by '\t+9 characters'
IFS=$(printf '\t')
seems to have done the trick.
#Gairfowl hinted in the right direction.
I hadn't grasped, that the tenth character in the path was a t.
Thank you very much!
I need to display all the bytes from and ELF file to a QTextEdit and i did not find any reasonable way to do this. I could print maximum "?ELF??" then nothing. The content of the ELF is read in a char* array (this is a requirement, can't change that) and yes, for sure the content is read.
I am guessing that your code looks something like this:
char *elf = ReadElfFile();
QString str(elf); // Constructs a string initialized with the 8-bit string str.
QTextEdit edit(str);
The problem is that QString constructor will stop on first NUL character, and the ELF file is full of them.
If you want to make a QString that contains NULs, do something like this:
QString str(QByteArray(elf, length_of_elf));
This just nearly broke me too, so I'll post my solution to anyone interested.
Let's say I have a QByteArray data that is filled like so
data += file.readAll();
I'll then invoke an update of the QTextEdit where I'll do
QByteArray copy = data;
QString text = copy.replace((char)0x00, "\\0");
textEdit.setPlainText(text);
This way, all null bytes in the data will be displayed as the printable string \0.
Since I want changes of the textEdit to be reflected in my data, I have to parse this back using
QByteArray hex = textEdit.toPlainText().toUtf8().toHex().toUpper();
hex.replace("5C30", "00");
hex.replace("5C00", "5C30"); // oops, was escaped
data = QByteArray::fromHex(hex);
I'm using the hex format because I just could not get the replace to work with null byte characters. The code above first replaces all occurrences of the string \0 with null bytes in the data. Then it replaces any \ followed by a null byte back with \0 - which essentially means \\0 becomes \0.
It's not very elegant, but maybe it helps anyone ending up here to move on in the right direction. If you have improvements, please comment.
In my program the user can either provide a filename on the command line or using a QFileDialog. In the first case, I have a char* without any encoding information, in the second I have a QString.
To store the filename for later use (Recent Files), I need it as a QString. But to open the file with std::ifstream, I need a std::string.
Now the fun starts. I can do:
filename = QString::fromLocal8Bit(argv[1]);
later on, I can do:
std::string fn = filename.toLocal8Bit().constData();
This works for most characters, but not all. For example, the word Раи́са will look the same after going through this conversion, but, in fact, have different characters.
So while I can have a Раи́са.txt, and it will display Раи́са.txt, it will not find the file in the filesystem. Most letters work, but и́ doesnt.
(Note that it does work correctly when the file was chosen in the QFileDialog. It does not when it originated from the command line.)
Is there any better way to preserve the filename? Right now I obtain it in whatever native encoding, and can pass-on in the same encoding, without knowing it. At least so I thought.
'и́' is not an ASCII character, that is to say it has no 8-bit representation. How it is represented in argv[1] then is OS dependent. But it's not getting represented in just one char.
The fromLocal8bit uses the same QTextCodec::codecForLocale as toLocal8bit. And as you say your std::string will hold "Раи́са.txt" so that's not the problem.
Depending on how your OS defined std::ifstream though std::ifstream may expect each char to be it's own char and not go through the OS's translation. I expect that you are on Windows since you are seeing this problm. In which case you should use the std::wstring implementation of std::fstream which is Microsoft specific: http://msdn.microsoft.com/en-us/library/4dx08bh4.aspx
You can get a std::wstring from QString by using: toStdWString
See here for more info: fstream::open() Unicode or Non-Ascii characters don't work (with std::ios::out) on Windows
EDIT:
A good cross-platform option for projects with access to it is Boost::Filesystem. ypnos Mentions File-Streams as specifically pertinent.