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ToString

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

ToString[expr]

gives the printed form of expr (as OutputForm) as a String; strings inside expr appear without quotes, ToString["s"] is "s".

ToString[expr, form]

uses the specified output form.

Notes Supported forms: OutputForm (default, linear), InputForm, FullForm, TeXForm.

Examples (16)

Every input below was run against the current Mathilda build and its output recorded.

Basic examples (5)

In[1]:= ToString[x^2 + y^3]
Out[1]= "x^2 + y^3"

In[2]:= ToString[x^2 + y^3, FullForm]
Out[2]= "Plus[Power[x, 2], Power[y, 3]]"

In[3]:= ToString[x^2 + y^3, TeXForm]
Out[3]= "x^{2}+y^{3}"

In[4]:= ToString[{"a", 1}]
Out[4]= "{a, 1}"

In[5]:= ToString["a\"b", InputForm]
Out[5]= "\"a\\\"b\""

Applications (11)

The default is OutputForm

In[6]:= ToString[x^2 + y^3]
Out[6]= "x^2 + y^3"

A string is its own OutputForm: no added quotes

In[7]:= ToString["hello"]
Out[7]= "hello"

Strings inside an expression print as their characters

In[8]:= ToString[{"a", 1}]
Out[8]= "{a, 1}"

Under InputForm, quotes and backslashes are escaped

In[9]:= ToString["a\"b", InputForm]
Out[9]= "\"a\\\"b\""

The internal tree

In[10]:= ToString[{1, "a"}, FullForm]
Out[10]= "List[1, \"a\"]"

TeX for typesetting

In[11]:= ToString[x^2 + y^3, TeXForm]
Out[11]= "x^{2}+y^{3}"

Rule-delayed stays distinct from rule

In[12]:= ToString[a :> b, TeXForm]
Out[12]= "a:\\to b"

A generated constant becomes a subscript

In[13]:= ToString[C[10], TeXForm]
Out[13]= "c_{10}"

The decimal digits of 2^100

In[14]:= StringLength[ToString[2^100]]
Out[14]= 31

The InputForm text reads back

In[15]:= ToExpression[ToString[(a + b)^2/c, InputForm]] === (a + b)^2/c
Out[15]= True

An unknown form stays unevaluated

In[16]:= ToString[x, FooForm]
Out[16]= ToString[x, FooForm]

Implementation notes

Algorithm. builtin_tostring (src/core.c) renders its argument to a string through the shared printer in src/print.c. It takes 1ā€“2 arguments, and the second must be a form symbol. As in Mathematica, the default form is OutputForm (since v0.455; before that it was InputForm). A string argument comes back as itself, with no render and no quotes. Anything else goes through expr_to_string_outputform, which prints strings anywhere in the tree as their characters (ToString[{"a", 1}] is "{a, 1}"). The other forms select a printer:

  • InputForm and StandardForm use expr_to_string, which keeps string quotes and escapes " and \, so the result reads back.
  • FullForm uses expr_to_string_fullform.
  • TeXForm wraps the argument in TeXForm[...] and prints that. This sets C[k] as c_k and infix heads as \to, :\to, \land, ā€¦

Data structures. The printer writes into a heap buffer, a tmpfile() round trip on _WIN32. The buffer is copied into a fresh EXPR_STRING. Precedence-aware parenthesisation, Rational/Complex printing and the infix StringExpression/Pattern/Repeated forms ("a"~~x_, x:p, p..) all come from print_standard.

Complexity / limits. Linear in the size of the printed form. Mathilda's OutputForm is one-dimensional (ToString[1/2] is "1/2"), whereas Mathematica's is a 2-D layout. An unknown form such as ToString[x, FooForm] leaves the call unevaluated, so a typo shows at the call site. Protected.

  • Protected.
  • An unsupported form leaves the call unevaluated (e.g. ToString[x, FooForm] returns ToString[x, FooForm]), so a typo is visible at the call site rather than silently downgraded.
  • TeXForm renders the generated constant C[k] (from DSolve, Reduce, Integrate) as the subscripted c_k, matching Mathematica: ToString[C[1], TeXForm] is "c_1", and ToString[C[10], TeXForm] is "c_{10}" (single-character subscripts bare, longer ones braced). The same holds for the notebook LaTeX renderer.
  • TeXForm sets the infix heads infix: Rule as \to, RuleDelayed as :\to, Set as =, SetDelayed as :=, And/Or as \land/\lor, the relations as =, \neq, <, >, \leq, \geq, SameQ/UnsameQ as \equiv/\not\equiv, Not as \neg, and a chained Inequality as the chain (1<x<2). RuleDelayed is deliberately distinguished from Rule ā€” one glyph for both would make a -> b and a :> b indistinguishable once typeset, the same reason SetDelayed is :=. The notebook LaTeX renderer agrees, and additionally brackets a nested operator that binds looser than the one holding it ((a || b) && c, but not a && b || c).

Attributes: Protected.

References

See also: String, InputForm, FullForm, TeXForm, StandardForm, DSolve, Reduce, Integrate

Notes & additional examples

Notes

  • Since v0.455 ToString[expr] uses OutputForm by default, as Mathematica does, so strings come out without quotes: ToString["hello"] is "hello". It used to be "\"hello\"".
  • The supported forms are OutputForm (the default), InputForm, FullForm and TeXForm. StandardForm is accepted as an alias of InputForm. InputForm keeps string quotes and escapes " and \, so the result can be read back with ToExpression.
  • Mathilda's OutputForm is one-dimensional (ToString[1/2] is "1/2"), whereas Mathematica's is a 2-D layout.
  • Under TeXForm the generated constants C[k] render as c_k (single characters bare, longer subscripts braced), and Rule/RuleDelayed render as \to / :\to.
  • An unknown form leaves the call unevaluated, so a typo shows at the call site. Protected.
  • See also: ToExpression, InputForm, FullForm, TeXForm, StringJoin.