Span

Mon, 27 Apr 2026 00:00:00 +0000

std::span is a class template introduced in C++ 20. As one of the most paramount features, span is essentially a non-owning view of a sequence of objects, which is contiguously distributed in memory and can consequently be iterated and indexed, e.g., std::array, std::vector, std::string.

Constructors

span(ptr)
span(ptr, len)
span(starting_ptr, ending_ptr)

Member functions

first(num) returns a new span comprising the first num elements.
last(num) returns a new span comprising the last num elements.
front() / data() returns a reference to the first element.
back() returns a reference to the last element.
at(idx) / operator[idx] returns a reference to the idx th element.
subspan(starting_idx, len) returns a new span of length len starting from starting_idx th element.
size() returns the number of elements in the span.
empty() returns a boolean indicator whether the span is empty.
begin() returns the iterator to the beginning of the span.
end() returns the iterator to the ending (sentinel) of the span.

Armadillo

Wed, 15 Oct 2025 00:00:00 +0000

Introduction

Armadillo¹ is an excellent C++ library, which provides efficient linear algebra related operations, based on a series of classes, e.g., for vectors, matrices, etc. Thanks to its friendly interfaces, similar to MATLAB, the library is very easy to use.

Armadillo is developped by Conrad Sanderson and Ryan Curtin, and released under Apache 2.0 license.

Installation & configuration

Installation

Above all, several third-party open source libraries (including OpenBLAS, LAPACK, ARPACK, SuperLU) should be installed as necessary dependencies. Taking ArchLinux for instance, these libraries can be simply installed by

 pacman -S openblas lapack arpack superlu

Then, armadillo can be installed by executing following commands.

 git clone --depth 1 https://gitlab.com/conradsnicta/armadillo-code.git
 cd armadillo-code
 cmake . -DCMAKE_INSTALL_PREFIX:PATH=/opt/armadillo
 make
 make install

Configuration

Create file /etc/ld.so.conf.d/arma.conf with its content as follows.
```
 /opt/armadillo/lib
```
Then, fresh the cache accordingly.
```
 ldconfig
```

Create a soft link for headers.

 ln -s /opt/armadillo/include/* /usr/local/include/

Building & linking

Due to the soft links in /usr/local/include, the headers can already be found.
Due to /etc/ld.so.conf.d/arma.conf, the object files in the library can be directly linked by option -larmadillo, e.g.,
```
 g++ main.cpp -o main -O2 -std=c++14 -larmadillo
```

Cpp on Shaka