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I want to know how the string manipulation functions are implemented internally so I can figure out their performance. Is there a way to find this out?
I'm talking about null-terminated c strings (arrays of chars) and the related functions (strcat and such) in C++, if that has anything to do with it.
Is there a way to find this out?
Use the source, Luke
The sources for GNU libc string functions are easily viewable in the Git repository
You can also look at other free software or open source C libraries, such as newlib, FreeBSD, NetBSD, OpenBSD, OpenSolaris etc.
if your whole purpose is to figure out the performance I don't think you need to know how it is implemented. You can feed in different data and come up with a graph and compare how the functions performed.
But if you need to study how those functions are implemented, then there is always the source code, which you can get from the internet for different C++ compilers( Not all compilers though).
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I am trying to convert some code written in MATLAB to C++. I'm having some (or actually quite a lot of) trouble finding an alternative to the "fminunc" function which is used in the MATLAB code that I can replace and use in the C++ code. I've been looking at the "dlib"-library because I've heard it could be a function there I can use, but I'm not sure what function to use.
This is how the "fminunc" is used in the MATLAB code I want to convert:
[theta, cost] = ...
fminunc(#(t)(costFunction(t, X, y)), initial_theta, options);
Does anyone know any good optimizing functions like this in C++?
I believe what you are looking for is Google's Ceres Solver, an open source C++ library for modeling and solving large, complicated optimization problems. The code is designed to handle two classes of problems:
Non-linear Least Squares problems with bounds constraints.
General unconstrained optimization problems.
Automatic Differentiation is also supported.
Several cool example applications can be found here.
There are a bunch of optimizers in dlib, some that use gradients and others than just work on black-box functions. You can see some examples here http://dlib.net/optimization_ex.cpp.html and more generally here http://dlib.net/optimization.html.
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I'm a beginner C++ programmer.I would like to know that Is it possible to output to console windows without using iostream header file?
the answer of the question is actually Yes ! but How?
You can always delve down to the C library level, using e.g. printf.
If you don't want to use the standard library at all then you have to use platform-specific functionality. In Windows there are many layers here, much like the C++ versus C layers in the standard library. The highest Windows API layer is the WriteFile function, and below that, WriteConsole, then perhaps WriteConsoleOutput, so on, check it out.
Note that there are at least two open source projects to provide more reasonable console functionality in Windows, namely Console2 at SourceForge and mintty at Google Code.
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I am wanting to have a go at a C++ parser for a formatter I am making.
You can obviously open a file and use getline(..) or get(), is this reasonable way of starting things off and then working out a system using vector arrays and hence creating loads of arrays and somehow structuring out and processing what you are doing from there. For example say I wanted to find ever function in a source file, all functions have the common syntax, "(){" once whitespace has been removed, so do you just look for common delimeters to parse out the sections into arrays. I suppose I will learn as I go.
Or I also assume there are tried and tested ways of doing this, and I would likley just be reinventing the wheel as they say.
C++ is a language that is quite hard to parse in the first place. So if you want anything other that really trivial C++ code to be "understood" by your parser, you are definitely better off starting with an existing product.
The Clang frontend library would perhaps be a good starting point.
There are also a number of "source to source" conversion examples based on clang. Here's one of them: http://eli.thegreenplace.net/2012/06/08/basic-source-to-source-transformation-with-clang/
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I have seen recently that people use xml files as a database to store the settings. However, I don't know why exactly is it done. I am from a C/C++, Linux background. Thus, please help me to understand this concept. Any simple C/C++ example will help me to understand it's benefit better?
XML is a very common tool with tons of libraries to handle it. Although it isn't the most beautiful format in the world, it is possible to read and modify it by both hand and program. Probably one want to use it when program configuration modified by some gui or tool. If you intend manual configuration, it's probably better to choose something else, for example ini. This is why linux tools rarely use XML, BTW.
As a C++ programmer you'd probably find interesting the "boost::property_tree" library to deal with configs. Examples of usage included in the documentation. Also it provides with plenty of different backends to store configuration, so you haven't to stick to some one format.
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I'm creating a program that make some matrix analysis. Now i want to implement some basic algorithms but I need to allow users implement new algorithms in the future without recompile the code.
I suppose that these algorithms already exist, probably in c/c++ language.
How can I do it if I use qt?
Maybe it's better use an other programming language and why?
I suppose that these algorithms already exist, probably in c/c++ language
If that's so, one way would be to write your program capable of loading DLLs, and then your users can compile their own algorithm DLL plugins for your application.
Or if you don't expect your users to be able to compile the existing c/c++ algorithms, maybe you can do as Joachim Pileborg suggests, and add in a scripting interface.