FMt

fmt is a standard library package in the Go programming language that provides formatted I/O. It supports writing to and reading from various streams through interaction with io.Writer and io.Reader, making it a central tool for output, input, and string construction in Go programs.

The package offers a set of printing functions such as Print, Println, and Printf for writing to a destination, and their variants Fprint, Fprintln, and Fprintf that take an explicit writer. For building strings without printing, there are Sprint, Sprintf, and Sprintln. On the input side, fmt provides scanning functions like Scan, Scanln, and Scanf, along with Fscan, Fscanln, and Fscanf for reading from specific readers into provided variables.

Formatting is driven by verbs that determine how values are represented. Common verbs include %v for a default representation, %#v for Go-syntax representation, and %T for the type. Numeric formats include %d, %b, %o, %x, and %X; floating-point forms use %f, %e, and %g. Strings use %s, and quoted strings use %q. Pointers use %p, booleans use %t, and characters use %c. Additional features include width and precision specifiers (for alignment and decimal places) and flags such as − for left alignment, + for sign, and 0 for zero padding. The verbs can also print the type with %T and the Go-syntax representation with %#v.

fmt is widely used for logging, user-facing messages, and parsing simple input, and it is essential for producing consistent, human-readable output across Go programs.