# 7.3: String Formatting


## 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.