Skip to main content
Engineering LibreTexts

7.3: String Formatting

  • Page ID
    10702
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)

    Overview

    String formatting uses a process of string interpolation (variable substitution) to evaluate a string literal containing one or more placeholders, yielding a result in which the placeholders are replaced with their corresponding values.[1]

    Discussion

    Most current programming languages provide one or more string formatting functions that use a template string with placeholders and optional alignment, width, and precision indicators to generate formatted output.

    Language Function Examples
    C++ snprintf() snprintf(str, sizeof(str), "Hello %s!", name);
    snprintf(str, sizeof(str), "$%.2f", value);
    C# Format() String.Format("Hello {0}!", name);
    String.Format("{0:$0.00}", value);
    Java format() String.format("Hello %s!", name);
    String.format("$%.2f", value);
    JavaScript template literal `Hello ${name}`;
    `$${value.toFixed(2)}`;
    Python format() "Hello {}!".format(name)
    "${:.2f}".format(value)
    Swift interpolation
    String()
    "Hello \(name)!"
    String(format:"%.2f", value)

    String interpolation, like string concatenation, may lead to security problems. If user input data is improperly escaped or filtered, the system may be exposed to code injection.[2]

    Key Terms

    code injection
    The exploitation of a computer bug that is caused by processing invalid data.[3]
    formatting
    Modifying the way the output is displayed.
    string interpolation
    Evaluating a string literal containing one or more placeholders, yielding a result in which the placeholders are replaced with their corresponding values.

    References


    1. Wikipedia: String interpolation
    2. Wikipedia: String interpolation
    3. Wikipedia: Code injection

    7.3: String Formatting is shared under a CC BY-SA license and was authored, remixed, and/or curated by LibreTexts.

    • Was this article helpful?