what's the best way to add multilanguage support to a C++ program?
If possible, the language should be read in from a plain text file containing something like key-value pairs (§WelcomeMessage§ "Hello %s!").
I thought of something like adding a localizedString(key) function that returns the string of the loaded language file. Are there better or more efficient ways?
//half-pseudo code
//somewhere load the language key value pairs into langfile[]
string localizedString(key)
{
//do something else here with the string like parsing placeholders
return langfile[key];
}
cout << localizedString(§WelcomeMessage§);
Simplest way without external libraries:
// strings.h
enum
{
LANG_EN_EN,
LANG_EN_AU
};
enum
{
STRING_HELLO,
STRING_DO_SOMETHING,
STRING_GOODBYE
};
// strings.c
char* en_gb[] = {"Well, Hello","Please do something","Goodbye"};
char* en_au[] = {"Morning, Cobber","do somin'","See Ya"};
char** languages[MAX_LANGUAGES] = {en_gb,en_au};
This will give you what you want. Obviously you could read the strings from a file. I.e.
// en_au.lang
STRING_HELLO,"Morning, CObber"
STRING_DO_SOMETHING,"do somin'"
STRING_GOODBYE,"See Ya"
But you would need a list of string names to match to the string titles. i.e.
// parse_strings.c
struct PARSE_STRINGS
{
char* string_name;
int string_id;
}
PARSE_STRINGS[] = {{"STRING_HELLO",STRING_HELLO},
{"STRING_DO_SOMETHING",STRING_DO_SOMETHING},
{"STRING_GOODBYE",STRING_GOODBYE}};
The above should be slightly easier in C++ as you could use the enum classes toString() method (or what ever it as - can't be bothered to look it up).
All you then have to do is parse the language files.
I hope this helps.
PS: and to access the strings:
languages[current_language][STRING_HELLO]
PPS: apologies for the half c half C++ answer.
Space_C0wb0w's suggestion is a good one. We currently use successfully use ICU for that in our products.
Echoing your comment to his answer: It is indeed hard to say that ICU is "small, clean, uncomplicated". There is "accidental" complexity in ICU coming from its "Java-ish" interface, but a large part of the complexity and size simply comes from the complexity and size of the problem domain it is addressing.
If you don't need ICU's full power and are only interested in "message translation", you may want to look at GNU gettext which, depending on your platform and licencing requirements, may be a "smaller, cleaner and less-complicated" alternative.
The Boost.Locale project is also an interesting alternative. In fact, its "Messages Formatting" functionality is based on the gettext model.
Since you are asking for the best way (and didn't mention the platform) I would recommend GNU Gettext.
Arguably it is the most complete and mature internationalization library for C/C++ programming.
Related
I'm pretty new to C++ programming but for certain reasons I need to develop a small tool in C++. I've written the same tool in C# already. Right now I'm trying to check if my string contains a value that is stored in a std::vector. In C# this is pretty straight forward, simply using something like this:
if(string.Contains(myarray)) { // do sth. }
In C++ this seems way harder to achieve. I googled quite a bit but so far I found only solutions to check if the WHOLE string exists in an array and not just a certain part of it.
Unfortunately std::string does not have a method that can see if a element of a vector is in a string like C# does. What it does have though is std::string::find which can determine if a string is contained within the string you call find on. You could use that like
std::vector<std::string> words;
// fill words
std::string search_me = "some text";
for (const auto & e : words)
{
if (search_me.find(e) != std::string::npos)
{
// e is contained in search me. do something here
// call break here if you only want to check for one existence
}
}
This is O(N*complexity_of_find).
Use a for loop and the find method.
I would suggest std::find_first_of
Not sure if I understood your exact problem, though. Could you give a small example of what your are trying to find in what?
If you need more effective way to find several substrings in string than straightforward find string-by-string, you can use Aho-Corasick algorithm
It uses trie to hold substrings. First google link to c++ implementation
I am attempting to construct a serial number of a certain format. This number will be entered into a database. At this point I am having to use sprintf, but I would like a native C++ method for it.
Here is sample code:
int i;
sprintf(buffer, "%03d", i);
The integer will be anywhere from 1 to 3 digits. The format needs to look like this:
001, ... 013, ... 101, ... etc.
The "serial number" has the format:
AAAAA001, ... AAAAA013, ... AAAAA101, etc.
So the question is, is there a way to do this that is native to C++ without having to use iostream manipulators and that is included in the mingw-w64 libraries. Or does it require something like boost libraries?
Another way to put it: is there a drop-in replacement in C++ for the C sprintf function?
Edit based upon comments:
So there is nothing as simple as....
int i;
string buffer;
sprintf(buffer, "%03d", i);
I realize that this does not work, but it gives the thought anyway. There is no way to operate directly on a string class object with a method that serves the function of sprintf?
I'm taking aruisdante's answer as the best answer to the question although it is a stream which I initially found undesirable.
I think the real question you have to answer first is "why do you not want >to use sstream "? Without establishing that first, it's a bit of an >XYProblem, since sstream will certainly solve the given problem clearly, >type-safely and relatively efficiently. – aruisdante
My understanding of streams was too narrow. It looks like a stringstream should work well for my application.
Thanks again.
Ok, first of all I don't want to use Boost, or any external libraries. I just want to use the C++ Standard Library. I can easily split strings with a given delimiter with my split() function:
void split(std::string &string, std::vector<std::string> &tokens, const char &delim) {
std::string ea;
std::stringstream stream(string);
while(getline(stream, ea, delim))
tokens.push_back(ea);
}
I do this on filenames. But there's a problem. There are files that have extensions like: tar.gz, tar.bz2, etc. Also there are some filenames that have extra dots. Some.file.name.tar.gz. I wish to separate Some.file.name and tar.gz Note: The number of dots in a filename isn't constant.
I also tried PathFindExtension but no luck. Is this possible? If so, please enlighten me. Thank you.
Edit: I'm very sorry about not specifying the OS. It's Windows.
I think you could use std::string find_last_of to get the index of the last ., and substr to cut the string (although the "complex extensions" involving multiple dots will require additional work).
There is no way of doing what you want that does not involve a database of extensions for your purpose. There's nothing magical about extensions, they are just part of a filename (if you gunzip foo.tar.gz you'll likely get a foo.tar, so for this application .gz actually is "the extension"). So, in order to do what you want, build a database of extensions that you want to look for and fall back on "last dot" if you don't find one.
There's nothing in the C++ standard library -- that is, it's not in the Standard --, but every operating system I know of provides this functionality in a variety of ways.
In Windows you can use _splitpath(), and in Linux you can use dirname() & basename()
The problem is indeed filenames like *.tar.gz, which can not be split consistently, due to the fact that (at least in Windows) the .tar part isn't part of the extension. You'll either have to keep a list for these special cases and use a one-dot string::rfind for the rest or find some pre-implemented way. Note that the .tar.* extensions aren't infinite, and very much standardized (there's about ten of them I think).
You could create a look-up table of file extensions that you think you might encounter. And also add a command line option to add a new one to the look-up table if you encounter anything new. Then parse through the file name to see if it any entry in the look-up table is a sub-string in the file name.
EDIT: You can also refer to this question: C++/STL string: How to mimic regex like function with wildcards?
I'm wondering if there is a library like Boost Format, but which supports named parameters rather than positional ones. This is a common idiom in e.g. Python, where you have a context to format strings with that may or may not use all available arguments, e.g.
mouse_state = {}
mouse_state['button'] = 0
mouse_state['x'] = 50
mouse_state['y'] = 30
#...
"You clicked %(button)s at %(x)d,%(y)d." % mouse_state
"Targeting %(x)d, %(y)d." % mouse_state
Are there any libraries that offer the functionality of those last two lines? I would expect it to offer a API something like:
PrintFMap(string format, map<string, string> args);
In Googling I have found many libraries offering variations of positional parameters, but none that support named ones. Ideally the library has few dependencies so I can drop it easily into my code. C++ won't be quite as idiomatic for collecting named arguments, but probably someone out there has thought more about it than me.
Performance is important, in particular I'd like to keep memory allocations down (always tricky in C++), since this may be run on devices without virtual memory. But having even a slow one to start from will probably be faster than writing it from scratch myself.
The fmt library supports named arguments:
print("You clicked {button} at {x},{y}.",
arg("button", "b1"), arg("x", 50), arg("y", 30));
And as a syntactic sugar you can even (ab)use user-defined literals to pass arguments:
print("You clicked {button} at {x},{y}.",
"button"_a="b1", "x"_a=50, "y"_a=30);
For brevity the namespace fmt is omitted in the above examples.
Disclaimer: I'm the author of this library.
I've always been critic with C++ I/O (especially formatting) because in my opinion is a step backward in respect to C. Formats needs to be dynamic, and makes perfect sense for example to load them from an external resource as a file or a parameter.
I've never tried before however to actually implement an alternative and your question made me making an attempt investing some weekend hours on this idea.
Sure the problem was more complex than I thought (for example just the integer formatting routine is 200+ lines), but I think that this approach (dynamic format strings) is more usable.
You can download my experiment from this link (it's just a .h file) and a test program from this link (test is probably not the correct term, I used it just to see if I was able to compile).
The following is an example
#include "format.h"
#include <iostream>
using format::FormatString;
using format::FormatDict;
int main()
{
std::cout << FormatString("The answer is %{x}") % FormatDict()("x", 42);
return 0;
}
It is different from boost.format approach because uses named parameters and because
the format string and format dictionary are meant to be built separately (and for
example passed around). Also I think that formatting options should be part of the
string (like printf) and not in the code.
FormatDict uses a trick for keeping the syntax reasonable:
FormatDict fd;
fd("x", 12)
("y", 3.141592654)
("z", "A string");
FormatString is instead just parsed from a const std::string& (I decided to preparse format strings but a slower but probably acceptable approach would be just passing the string and reparsing it each time).
The formatting can be extended for user defined types by specializing a conversion function template; for example
struct P2d
{
int x, y;
P2d(int x, int y)
: x(x), y(y)
{
}
};
namespace format {
template<>
std::string toString<P2d>(const P2d& p, const std::string& parms)
{
return FormatString("P2d(%{x}; %{y})") % FormatDict()
("x", p.x)
("y", p.y);
}
}
after that a P2d instance can be simply placed in a formatting dictionary.
Also it's possible to pass parameters to a formatting function by placing them between % and {.
For now I only implemented an integer formatting specialization that supports
Fixed size with left/right/center alignment
Custom filling char
Generic base (2-36), lower or uppercase
Digit separator (with both custom char and count)
Overflow char
Sign display
I've also added some shortcuts for common cases, for example
"%08x{hexdata}"
is an hex number with 8 digits padded with '0's.
"%026/2,8:{bindata}"
is a 24-bit binary number (as required by "/2") with digit separator ":" every 8 bits (as required by ",8:").
Note that the code is just an idea, and for example for now I just prevented copies when probably it's reasonable to allow storing both format strings and dictionaries (for dictionaries it's however important to give the ability to avoid copying an object just because it needs to be added to a FormatDict, and while IMO this is possible it's also something that raises non-trivial problems about lifetimes).
UPDATE
I've made a few changes to the initial approach:
Format strings can now be copied
Formatting for custom types is done using template classes instead of functions (this allows partial specialization)
I've added a formatter for sequences (two iterators). Syntax is still crude.
I've created a github project for it, with boost licensing.
The answer appears to be, no, there is not a C++ library that does this, and C++ programmers apparently do not even see the need for one, based on the comments I have received. I will have to write my own yet again.
Well I'll add my own answer as well, not that I know (or have coded) such a library, but to answer to the "keep the memory allocation down" bit.
As always I can envision some kind of speed / memory trade-off.
On the one hand, you can parse "Just In Time":
class Formater:
def __init__(self, format): self._string = format
def compute(self):
for k,v in context:
while self.__contains(k):
left, variable, right = self.__extract(k)
self._string = left + self.__replace(variable, v) + right
This way you don't keep a "parsed" structure at hand, and hopefully most of the time you'll just insert the new data in place (unlike Python, C++ strings are not immutable).
However it's far from being efficient...
On the other hand, you can build a fully constructed tree representing the parsed format. You will have several classes like: Constant, String, Integer, Real, etc... and probably some subclasses / decorators as well for the formatting itself.
I think however than the most efficient approach would be to have some kind of a mix of the two.
explode the format string into a list of Constant, Variable
index the variables in another structure (a hash table with open-addressing would do nicely, or something akin to Loki::AssocVector).
There you are: you're done with only 2 dynamically allocated arrays (basically). If you want to allow a same key to be repeated multiple times, simply use a std::vector<size_t> as a value of the index: good implementations should not allocate any memory dynamically for small sized vectors (VC++ 2010 doesn't for less than 16 bytes worth of data).
When evaluating the context itself, look up the instances. You then parse the formatter "just in time", check it agaisnt the current type of the value with which to replace it, and process the format.
Pros and cons:
- Just In Time: you scan the string again and again
- One Parse: requires a lot of dedicated classes, possibly many allocations, but the format is validated on input. Like Boost it may be reused.
- Mix: more efficient, especially if you don't replace some values (allow some kind of "null" value), but delaying the parsing of the format delays the reporting of errors.
Personally I would go for the One Parse scheme, trying to keep the allocations down using boost::variant and the Strategy Pattern as much I could.
Given that Python it's self is written in C and that formatting is such a commonly used feature, you might be able (ignoring copy write issues) to rip the relevant code from the python interpreter and port it to use STL maps rather than Pythons native dicts.
I've writen a library for this puporse, check it out on GitHub.
Contributions are wellcome.
I'm learning C++ for one of my CS classes, and for our first project I need to parse some URLs using c-strings (i.e. I can't use the C++ String class).
The only way I can think of approaching this is just iterating through (since it's a char[]) and using some switch statements. From someone who is more experienced in C++ - is there a better approach? Could you maybe point me to a good online resource? I haven't found one yet.
Weird that you're not allowed to use C++ language features i.e. C++ strings!
There are some C string functions available in the standard C library.
e.g.
strdup - duplicate a string
strtok - breaking a string into tokens. Beware - this modifies the original string.
strcpy - copying string
strstr - find string in string
strncpy - copy up to n bytes of string
etc
There is a good online reference here with a full list of available c string functions
for searching and finding things.
http://www.cplusplus.com/reference/clibrary/cstring/
You can walk through strings by accessing them like an array if you need to.
e.g.
char* url="http://stackoverflow.com/questions/1370870/c-strings-in-c"
int len = strlen(url);
for (int i = 0; i < len; ++i){
std::cout << url[i];
}
std::cout << endl;
As for actually how to do the parsing, you'll have to work that out on your own. It is an assignment after all.
There are a number of C standard library functions that can help you.
First, look at the C standard library function strtok. This allows you to retrieve parts of a C string separated by certain delimiters. For example, you could tokenize with the delimiter / to get the protocol, domain, and then the file path. You could tokenize the domain with delimiter . to get the subdomain(s), second level domain, and top level domain. Etc.
It's not nearly as powerful as a regular expression parser, which is what you would really want for parsing URLs, but it works on C strings, is part of the C standard library and is probably OK to use in your assignment.
Other C standard library functions that may help:
strstr() Extracts substrings just like std::string::substr()
strspn(), strchr() and strpbrk() Find a character or characters in a string, similar to std::string::find_first_of(), etc.
Edit: A reminder that the proper way to use these functions in C++ is to include <cstring> and use them in the std:: namespace, e.g. std::strtok().
You might want to refer to an open source library that can parse URLs (as a reference for how others have done it -- obviously don't copy and paste it!), such as curl or wget (links are directly to their url parsing files).
I don't know what the requirements are for parsing the URLs,
but if this is CS level it would be appropriate to use (very
simple) BNF and a (very simple) recursive descent parser.
This would make for a more robust solution than direct
iteration, e.g. for malformed URLs.
Very few string functions from the standard C library would
be needed.
You can use C functions like strtok, strchr, strstr etc.
Many of the runtime library functions that have been mentioned work quite well, either in conjunction with or apart from the approach of iterating through the string that you mentioned (which I think is time honored).