Illya Starikov

After using a fairly large, matured language for a reasonable period of time, find peculiarities in the language or the libraries is guaranteed to happen. However, given it’s history, I have to say C++ definitely allows for some of the strangest peculiarities in it’s syntax. Below I list three that are my favorite.

Ternaries Returning lvalues

You might be familiar with ternaries as condition ? do something : do something else, and they become quite useful in comparison to the standard if-else. However, if you’ve dealt with ternaries a lot, you might have noticed that ternaries also return lvalues/rvalues. Now, as the name suggests suggests, you can assign to lvalues (lvalues are often referred to as locator values). So something like so is possible:

std::string x = "foo", y = "bar";

std::cout << "Before Ternary! ";
// prints x: foo, y: bar
std::cout << "x: " << x << ", y: " << y << "\n"; 

// Use the lvalue from ternary for assignment
(1 == 1 ? x : y) = "I changed";
(1 != 1 ? x : y) = "I also changed";

std::cout << "After Ternary! ";
// prints x: I changed, y: I also changed
std::cout << "x: " << x << ", y: " << y << "\n"; 

Although it makes sense, it’s really daunting; I can attest to never seeing it in the wild.

Commutative Bracket Operator

An interesting fact about C++ bracket operator, it’s simply pointer arithmetic. Writing array[42]() is actually the same as writing *(array + 42), and thinking in terms of x86/64 assembly, this makes sense! It’s simply an indexed addressing mode, a base (the beginning location of array) followed by an offset (42). If this doesn’t make sense, that’s okay. We will discuss the implications without any need for assembly programming.

So we can do something like *(array + 42), which is interesting; but we can do better. We know addition to be commutative, so wouldn’t saying *(42 + array) be the same? Indeed it is, and by transitivity, array[42]() is exactly the same as 42[array](). The following is a more concrete example.

std::string array[50];
42[array] = "answer";

// prints 42 is the answer
std::cout << "42 is the " << array[42] << ".";

Zero Width Space Identifiers

This one has the least to say, and could cause the most damage. The C++ standard allows for hidden white space in identifiers (i.e. variable names, method/property names, class names, etc.). So this makes the following possible.

int n​umber = 1;
int nu​mber = 2;
int num​ber = 3;

std::cout << n​umber << std::endl; // prints 1
std::cout << nu​mber << std::endl; // prints 2
std::cout << num​ber << std::endl; // prints 3

Using \u as a proxy for hidden whitespace character, the above code can be re-written as such:

int n\uumber = 1;
int nu\umber = 2;
int num\uber = 3;

std::cout << n\uumber << std::endl; // prints 1
std::cout << nu\umber << std::endl; // prints 2
std::cout << num\uber << std::endl; // prints 3

So if you’re feeling like watching the world burn, this would be the way to go.

The most frustrating thing about compiling LaTeX in a terminal is the wall of text that gets written to stdout. An easy solution would be piping to dev/null; except then you wouldn’t be able to get error messages (even if only pipe stdout to dev/null and keep stderr). So, I made a solution that handles the compiling by piping error messages to less. The syntax of latexerr FILENAME will compile the files. Passing --clean will delete temporary LaTeX files.

#!/bin/bash

# USAGE: ./script FILE --clean --glossary

extensions_to_delete=(\
	gz fls fdb_latexmk blg bbl log\
    aux out nav toc snm glg glo xdy
)

compile_and_open() {
    argument="$1"
    auxname="${argument%.tex}.aux"
    errors=$(pdflatex -shell-escape -interaction=nonstopmode -file-line-error "$argument" | grep ".*:[0-9]*:.*")

    if [[ -n $errors ]]; then
        echo "$1 Errors Detected"
        echo "$errors" | less
    else
        open_file $1
        echo "$1 Compile Successful"
    fi
}

open_file() {
    filename=`echo "$1" | cut -d'.' -f1`
    open "$filename.pdf"
    echo "$filename Opened"
}

# http://tex.stackexchange.com/questions/6845/compile-latex-with-bibtex-and-glossaries
glossary() {
    compile $1
    makeglossaries $1
    compile $1
    compile $1
}

clean() {
    for file in $(dirname $1)/*; do
        filename=$(basename "$file")
        extension="${filename##*.}"
        filename="${filename%.*}"

        for bad_extensions in "${extensions_to_delete[@]}" ; do
            if [[ $bad_extensions = $extension ]]; then
                rm $file
                echo "$file Deleted"
            fi
        done
    done
}

main() {
    compile_and_open $1

    if [ "$3" = "--glossary" ]; then
       glossary $1
    fi

    if [ "$2" = "--clean" ]; then
        clean $1
    fi

}

main "$@"

Updated version(s) will be posted here.