Illegal Parameter Number in Definition of currentlabelname to Be Read Again (2024)

Documents produced with the commands you lot have learned up to this bespeak will look acceptable to a large audience. While they are not fancy-looking, they obey all the established rules of good typesetting, which will brand them easy to read and pleasant to await at. However, there are situations where LaTeX does not provide a command or environment that matches your needs, or the output produced by some existing command may not encounter your requirements.

In this chapter, we will try to give some hints on how to teach LaTeX new tricks and how to brand it produce output that looks different from what is provided by default.

LaTeX is a fairly loftier-level language compared to Plain TeX and thus is more limited. The next chapter will focus on Plain TeX and will explain advanced techniques for programming.

To add your own commands, use the

  \newcommand { \name }[num]{definition} 

command. Basically, the command requires two arguments: the name of the command you desire to create (preceded by a backslash), and the definition of the command. Note that the control name can merely demand non be enclosed in braces, every bit yous like. The num argument in square brackets is optional and specifies the number of arguments the new command takes (upwardly to 9 are possible). If missing it defaults to 0, i.east. no argument immune.

The post-obit two examples should assist you to get the idea. The first example defines a new command called \wbal that volition print "The Wikibook about LaTeX". Such a control could come in handy if you had to write the title of this volume over and again.

  \newcommand { \wbal }{The Wikibook about \LaTeX } This is ''\wbal'' \ldots {} ''\wbal'' 

The next example illustrates how to define a new command that takes one argument. The #1 tag gets replaced past the argument you specify. If y'all wanted to use more than ane argument, apply #2 and so on, these arguments are added in an extra set up of brackets.

  \newcommand { \wbalsup }[i] { This is the Wikibook virtually LaTeX supported by #1} \newcommand { \wbalTwo }[2] { This is the Wikibook about LaTeX supported by #i and #2} % in the document body: \brainstorm {itemize} \item \wbalsup {Wikimedia} \item \wbalsup {lots of users!} \item \wbalTwo {John Doe}{Anthea Smith} \terminate {catalog} 

Name your new command \wbalTwo and not \wbal2 as digits cannot be used to name macros — invalid characters will fault out at compile-time.

LaTeX will non let you to create a new command that would overwrite an existing one. But there is a special command in example you explicitly want this: \renewcommand . Information technology uses the same syntax every bit the \newcommand command.

In certain cases you might also want to use the \providecommand command. Information technology works like \newcommand , but if the command is already divers, LaTeX will silently ignore the new command.

With LaTex2e, it is also possible to add together a default parameter to a command with the following syntax:

  \newcommand {name}[num][default]{definition} 

If the default parameter of \newcommand is present, then the outset of the number of arguments specified by num is optional with a default value of default; if absent, then all of the arguments are required.

  \newcommand { \wbalTwo }[2][Wikimedia]{ This is the Wikibook about LaTeX supported by {#1} and {#2}!} % in the document torso: \begin {catalog} \item \wbalTwo {John Doe} \item \wbalTwo [lots of users] {John Doe} \end {itemize} 

Note

When the command is used with an explicit first parameter it is given enclosed with brackets (here "[lots of users]").

Here is a common instance: if you are writing a book well-nigh Mathematics and you have to use vectors, yous take to decide how they will look. There are several different standards, used in many books. If a is a vector, some people like to add an pointer over it ( ${\displaystyle {\vec {a}}}$ ), other people write information technology underlined ( a ); another common version is to write it bold (a). Let united states assume you lot desire to write your vectors with an arrow over them; and so add together the post-obit line in your mystyle.sty.

  \newcommand { \myvec }[one]{ \vec {#1}} 

and write your vectors inside the new \myvec {...} command. Y'all can call it as you wish, just yous'd better choose a short name because you will probably write it very oftentimes. Then, if you lot modify your mind and you want your vectors to look differently you lot just have to alter the definition of your \myvec {...} . Use this approach whenever you can: this will salvage you a lot of fourth dimension and increase the consistency of your document.

DeclareRobustCommand Edit

Some commands are fragile, that is they fail in some environments. If a macro works in torso text but not in (for case) a figure caption, it's worth trying to replace the \newcommand { \MyCommand }... declaration with \DeclareRobustCommand { \MyCommand }... in the preamble. This is especially truthful for macros which, when expanded, produce text that is written to a .aux file.

But as with the \newcommand command, there is a command to create your own environments. The \newenvironment command uses the post-obit syntax:

  \newenvironment {name}[num][default]{before}{after} 

Once more \newenvironment can accept an optional argument. When the \begin {name} command (which starts the surround) is encountered, the textile specified in the before argument is processed earlier the text in the environment gets processed. The material in the after statement gets candy when the \cease {name} command (which ends the environment) is encountered.

The optional num and default arguments are used the same way as in the \newcommand control. LaTeX makes sure that you lot exercise not define an environs that already exists. If you ever want to modify an existing surround, you can use the \renewenvironment command. It uses the aforementioned syntax as the \newenvironment command.

The example beneath illustrates the usage of the \newenvironment control:

  \newenvironment {king} { \dominion {1ex}{1ex} \hspace { \stretch {ane}} } { \hspace { \stretch {one}} \dominion {1ex}{1ex} } \brainstorm {king} My humble subjects \ldots \end {king} 

Edit

When creating a new environment you may easily get bitten past extra spaces creeping in, which tin potentially have fatal effects. One example is when you lot want to create a championship surroundings which suppresses its ain indentation as well as the one on the post-obit paragraph. The \ignorespaces control in the begin block of the environment volition make it ignore any space subsequently executing the begin block. The finish block is a bit more tricky as special processing occurs at the end of an environment. With the \ignorespacesafterend LaTeX will upshot an \ignorespaces afterward the special 'end' processing has occurred.

  \newenvironment {simple} % { \noindent } % { \par\noindent } \brainstorm {simple} Run into the space\\to the left. \end {simple} Same\\here. 

 See the infinite to the left. Same here. 

  \newenvironment {correct} % { \noindent\ignorespaces } % { \par\noindent % \ignorespacesafterend } \brainstorm {correct} No space\\to the left. \end {correct} Same\\here. 

No space to the left. Aforementioned hither. 

Also, if yous're still having problems with extra space being appended at the end of your environs when using the \input for external source, make sure there is no infinite betwixt the beginning, sourcing, and cease of the environment, such as:

  \brainstorm {right} \input {somefile.tex} \cease {correct} 

or

  \brainstorm {right} % \input {somefile.tex} % \end {right} 

New commands tin can be declared within newenvironment. Commands declared within the newenvironment refer to their arguments by doubling the # character. In the following instance, a new environment is alleged along with a nested control:

  \newenvironment {topics}{ \newcommand { \topic }[two]{ \item {##i / ##ii} } Topics: \begin {itemize} } { \finish {itemize} } 

If, by mistake, the arguments passed to the \topics macro are defined with a single # character, the following error message will be thrown:

 ! Illegal parameter number in definition of \topics. 

The xkeyval packages will let you define central/value options for commands.

  \mycommand [key1=value1, key3=value3] {some text} 

The package is quite complete and documentation is exhaustive. Nosotros recommend that package developers read it. [1]

Let'southward provide a unproblematic example^[i]:

  \usepackage {xkeyval} % ... \makeatletter \def\my@emphstyle#1{ \csname my@mode@#1\endcsname } %% Predefined styles \providecommand\my@style@default{ \em } \providecommand\my@style@bold{ \bfseries } \define@key{myemph}{code}{ % \def\my@emphstyle{#1} } \define@key{myemph}{way}{ % \def\my@emphstyle{ \csname my@style@#ane\endcsname } } \newcommand\setemph [1] { % \setkeys {myemph}{#1} } \renewcommand\emph [1] { % { \my@emphstyle #i} } \makeatother Something \emph {important} \setemph {style=bold} Something \emph {important} \setemph {code=\Large\sffamily } Something \emph {important} 

LaTeX tin can manipulate numbers.

The calc package provides the common infix notation.

  \usepackage {calc} % ... \newcounter {mine} \setcounter {mine}{2*17} \themine 

For high-precision computations, yous tin use the fp ^[two] package.

  \usepackage {fp} % Clip \[  \FPmul\consequence { ii }{ 7 } \FPclip\issue\result  2 * 7   =   \result  \] % Infix \[  \newcommand\effect { 11 } \sqrt { \sin ( 2 + \result ) }  \approx  \FPeval\upshot {circular ( root ( 2 ,sin ( result  +   two . 5 )) , ii ) } \result  \] % Postfix \[  \FPupn\result { 17   2 . 5   +   17 . 5  swap  -   2   1   +   *   2  swap  / }  % or \FPupn\consequence{2 17.v 17 2.5 + - 2 1 + * /} \FPclip\upshot\result  ( 17 + ii . 5   -   17 . v )   *   ( 2 + 1 )   /   two   =   \result  \] % High precision \[  \FPdiv\result { 17 }{ 7 } \frac { 17 }{ 7 }  \approx   \FPtrunc\result\result { iii } \upshot  \] 

LaTeX can utilise conditionals thanks to the ifthen package.

  \usepackage {ifthen} % ... \ifthenelse { \equal { \myvar }{true} }{ This is truthful. }{ This is false. } 

FYI: For newer projects e-TeX is recommended^[3], bachelor in LaTeX from etoolbox. See section 3.6 of their manual.

Post-obit a short example, a bool that switches its state every time it is used.^[4]

  \documentclass {article} \usepackage {etoolbox} \usepackage {parskip} \usepackage {tikz} \newbool {volt} \newcommand { \onoff }{ % \ifbool {volt}{ % \boolfalse {volt} \candleOn\space ON}{ % \booltrue {volt} \candleOff\space OFF} % } \newcommand { \candleOff }{ \tikz \describe (0,0) rectangle (.2,.8);} \newcommand { \candleOn }{ \begin {tikzpicture} \draw (0,0) rectangle (.2,.8);\draw [fill=orange] (.1,.9) circle [radius=.1];\end {tikzpicture} } \brainstorm {certificate} \onoff\par \onoff\par \onoff\par \onoff\par \finish {document} 

The PGF/TikZ extension provides the \foreach command.

  \usepackage {tikz} % ... \foreach \i/\q in {wheat/50g, water/1L, yeast/2g}{ \noindent\i\dotfill\q\\ } 

If you are just using \foreach and not drawing graphics, you may instead use the pgffor package straight.

Alternatively y'all can check out the multido parcel.

xstring provides a lot of features. From CTAN:

• testing a string'southward contents
• extracting substrings
• substitution of substrings
• string length
• position of a substring
• number of recurrences of a substring

Examples:

  \usepackage {xstring} % ... \newcommand\mystr {Hello World!} The string ``\mystr'' has \StrLen { \mystr }{} characters. Predicate ``\mystr {} contains the word Hello'' is \IfSubStr { \mystr }{Howdy}{true}{false}. 

LaTeX provides two hooks:

• \AtBeginDocument volition let you specify a set of commands that will be executed when \begin {document} is met.
• \AtEndDocument does the same for \end {certificate} .

This gives you some more than flexiblity for macros. Information technology tin can be useful to override settings that get executed after the preamble. These hooks can be called several times. The commands volition be executed in the club they were set.

For example, let's replace the page numbers with oldstylenums:

  \usepackage {textcomp} \AtBeginDocument { % % Make the page numbers in text figures \let\myThePage\thepage \renewcommand { \thepage }{ \oldstylenums { \myThePage } } } 

At that place are as well hooks for classes and packages. Run across Creating Packages.

If you piece of work on a Unix-similar Bone, you might be using Makefiles or any kind of script to build your LaTeX projects. In that connection it might be interesting to produce unlike versions of the aforementioned document past calling LaTeX with command-line parameters. If you add the following structure to your document:

  \usepackage {ifthen} %... % default value. \providecommand\blackandwhite {faux} %... \ifthenelse { \equal { \blackandwhite }{true} }{ % "black and white" mode; practise something.. }{ % "colour" mode; practise something dissimilar.. } 

At present you lot tin can phone call LaTeX like this:

latex '\providecommand{\blackandwhite}{true}\input{test.tex}' 

Beginning the command \blackandwhite gets defined and then the actual file is read with input. Past setting \blackandwhite to false the color version of the document would exist produced.