Programming Fundamentals/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.

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.

Key Terms

code injection

The exploitation of a computer bug that is caused by processing invalid data.

formatting

Modifying the way the output is displayed.

interpolation

Variable substitution

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

• cnx.org: Programming Fundamentals – A Modular Structured Approach using C++

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