Format string
A format string is a character sequence containing literal text and directives that specify how supplied values are represented in formatted input or output.
Modern C, Third Edition
A format string is a character sequence containing literal text and format specifiers that controls formatted output conversion.
- How it is used
- Controls value conversion and placement in formatted C output, then extends to formatted input.
- How deep it goes
- Explains output specification fields and conversion choices, then contrasts input rules and format-string checking.
- Examples
- Uses an array-element printout, a three-double scanf call, and pointer-diagnostic output.
- What you can do after
- Apply it via printf, fprintf, and scanf while matching conversions to arguments and recognizing input-format pitfalls.
Modern C
A format string is a character sequence containing ordinary output text and conversion directives interpreted by a formatted-output function.
- How it is used
- Coordinates formatted output and input by mapping conversion directives to supplied values or destination pointers.
- How deep it goes
- Explains syntax, conversions, modifiers, whitespace, and undefined mismatches, but defers complete scanf conventions and deeper pointer details.
- Examples
- Demonstrates array-element output, numeric conversion choices, pointer diagnostics, and scanning three double values.
- What you can do after
- Apply it via C formatted-I/O functions while matching directives, argument types, conversions, and input behavior.
The Quick Python Book, Fourth Edition
A format string is a string containing replacement fields that specify how supplied values are incorporated into formatted text.
- How it is used
- Uses replacement fields to incorporate supplied values into formatted text, while distinguishing binary-record format strings used by `struct`.
- How deep it goes
- Works through field selection, escaped braces, alignment, padding, and dynamic width; defers the full format-specifier mini-language to standard-library documentation.
- Examples
- Compares short Python expressions that substitute words, escape braces, adjust padding, format decimals, and describe a binary record.
- What you can do after
- Apply it via `str.format()` to select and display values with basic alignment and padding.
Read how The Quick Python Book, Fourth Edition explains format string →
Python How-To
A format specifier is the portion of a formatting expression that controls how a value is represented, such as its precision or alignment.
- How it is used
- Controls f-string presentation so textual records and numeric values communicate clearly.
- How deep it goes
- Defines alignment, padding, width, precision, and numeric notation with worked examples, but does not descend into formatting internals.
- Examples
- Uses aligned task records, reusable format widths, formatted temperatures, percentages, scientific notation, and base conversions.
- What you can do after
- Apply it via Python f-strings to align text, control precision, and represent integers and floats in useful notations.
100 Java Mistakes and How to Avoid Them
A format string is a string containing directives that specify how values or text should be interpreted or formatted.
- How it is used
- Formats values for String.format() and PrintStream.printf() through directives embedded in a string.
- How deep it goes
- Explains specifier substitution, silent unused arguments, permissive %s and %b behavior, and static-analysis limits.
- Examples
- Uses point output, weekday and weekend status, greeting methods, and intentionally mismatched printf calls.
- What you can do after
- Diagnose/debug with it by aligning directives and arguments, checking permissive specifiers, and enabling targeted inspections.
Read how 100 Java Mistakes and How to Avoid Them explains format string →
Related concepts
- strftimeused by · strftime is a date-and-time formatting function or method that converts a temporal value into a string according to formatting directives.
- format methodused by · A format method is an API operation that produces a formatted representation by substituting supplied values into a formatting specification.
- scanf familyused by · The scanf family is a set of C standard-library functions that read formatted input, convert it according to a format string, and assign the results.
- format modifierhas part · A format modifier is an optional component of a formatted-input or formatted-output specification that conveys an argument’s size, length, or related type information.
- placeholderhas part · A placeholder is a temporary or symbolic stand-in for a value, content, component, or position that is supplied, replaced, or resolved later.
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