Sscan, Sscanf

Parsing in values from space-separated strings is a problem that has existed for many years. Even the earliest programmers may have struggled with this problem.

With Sscan and Sscanf, we can parse strings into multiple values. Sscan uses a space as a separator. And Sscanf uses a format string to guide its parsing.

Sscan example

Here we have a string that has values in it separated by spaces. We pass the correct number of arguments (as references) to fmt.Sscan. They are filled with the parsed values.

package main

import "fmt"

func main() {
    // Store values from Sscan in these locals.
    value1 := ""
    value2 := ""
    value3 := 0

    // Scan the 3 strings into 3 local variables.
    // ... Must pass in the address of the locals.
    _, err := fmt.Sscan("Bird frog 100", &value1, &value2, &value3);

    // If the error is nil, we have successfully parsed the values.
    if err == nil {
        // Print the values.
        fmt.Println("VALUE1:", value1);
        fmt.Println("VALUE2:", value2);
        fmt.Println("VALUE3:", value3);
    }
}
VALUE1: Bird
VALUE2: frog
VALUE3: 100

Sscanf

With this method, we must specify a format string to guide the parsing of the values. We can use standard format codes in the format string.

package main

import "fmt"

func main() {
    value1 := 0
    value2 := ""
    value3 := 0

    // Use format string to parse in values.
    // ... We parse 1 number, 1 string and 1 number.
    _, err := fmt.Sscanf("10 Bird 5", "%d %s %d", &value1, &value2, &value3);

    if err == nil {
        fmt.Println("VALUE1:", value1);
        fmt.Println("VALUE2:", value2);
        fmt.Println("VALUE3:", value3);
    }
}
VALUE1: 10
VALUE2: Bird
VALUE3: 5

Sscan versus split

With split() or fields() we can separate values and parse them. This has some advantages over Sscan, particularly for oddly-formed strings.

A review

With fmt.Sscan and Sscanf we have built-in parsing methods for strings that contain multiple values. These methods, when used correctly, can simplify programs.