Golang strconv.ParseFloat

last modified April 20, 2025

This tutorial explains how to use the strconv.ParseFloat function in Go. We'll cover string-to-float conversion basics with practical examples.

The strconv.ParseFloat function converts a string to a floating-point number. It's essential for parsing numeric input that may contain decimal points.

ParseFloat accepts strings representing floating-point numbers in decimal or scientific notation. It returns two values: the parsed float and an error. This follows Go's error handling pattern.

Basic strconv.ParseFloat Example

The simplest use of strconv.ParseFloat converts a numeric string to a float. Here we demonstrate successful conversion and error handling.

package main

import (
    "fmt"
    "strconv"
)

func main() {
    numStr := "3.1415"
    
    num, err := strconv.ParseFloat(numStr, 64)
    if err != nil {
        fmt.Println("Conversion error:", err)
        return
    }
    
    fmt.Printf("String '%s' converted to float %f\n", numStr, num)
}

We convert the string "3.1415" to a float64. The error is checked to handle cases where conversion fails. Successful conversion prints the floating-point value.

Handling Conversion Errors

strconv.ParseFloat returns an error for invalid numeric strings. This example shows proper error handling for different input cases.

package main

import (
    "fmt"
    "strconv"
)

func main() {
    testCases := []string{"3.14", "1.5e2", "abc", "123.45.67", ""}
    
    for _, tc := range testCases {
        num, err := strconv.ParseFloat(tc, 64)
        if err != nil {
            fmt.Printf("'%s' is not a valid float: %v\n", tc, err)
        } else {
            fmt.Printf("'%s' converted to %f\n", tc, num)
        }
    }
}

We test various string inputs, including valid and invalid cases. The error message helps identify why conversion failed for each invalid input.

Converting User Input

A common use case is converting command-line arguments or user input. This example demonstrates reading and converting numbers from standard input.

package main

import (
    "bufio"
    "fmt"
    "os"
    "strconv"
    "strings"
)

func main() {
    reader := bufio.NewReader(os.Stdin)
    
    fmt.Print("Enter a floating-point number: ")
    input, _ := reader.ReadString('\n')
    input = strings.TrimSpace(input)
    
    num, err := strconv.ParseFloat(input, 64)
    if err != nil {
        fmt.Println("Please enter a valid floating-point number")
        return
    }
    
    fmt.Printf("You entered: %f (square: %f)\n", num, num*num)
}

We read user input, trim whitespace, then attempt conversion. The program provides feedback for invalid input and demonstrates using the converted value.

Working with Different Bit Sizes

ParseFloat can return either float32 or float64 values based on the bitSize parameter. This example shows both approaches.

package main

import (
    "fmt"
    "strconv"
)

func main() {
    numStr := "123.45678901234567890"
    
    // 32-bit float
    num32, _ := strconv.ParseFloat(numStr, 32)
    fmt.Printf("32-bit float: %f\n", num32)
    
    // 64-bit float
    num64, _ := strconv.ParseFloat(numStr, 64)
    fmt.Printf("64-bit float: %f\n", num64)
    
    fmt.Printf("Precision difference: %.20f vs %.20f\n", num32, num64)
}

The bitSize parameter (32 or 64) determines the precision of the returned value. Float64 provides more precision but uses more memory than float32.

Scientific Notation Support

ParseFloat supports scientific notation. This example demonstrates converting numbers in scientific format.

package main

import (
    "fmt"
    "strconv"
)

func main() {
    scientificNumbers := []string{"1.23e3", "1.23E3", "1e-5", "-2.5e-2"}
    
    for _, sn := range scientificNumbers {
        num, err := strconv.ParseFloat(sn, 64)
        if err != nil {
            fmt.Printf("Failed to parse '%s': %v\n", sn, err)
        } else {
            fmt.Printf("'%s' = %f\n", sn, num)
        }
    }
}

Scientific notation (using 'e' or 'E') is commonly used for very large or very small numbers. ParseFloat handles both positive and negative exponents.

Alternative: fmt.Sscanf

fmt.Sscanf provides another way to parse floats from strings. This example compares it with ParseFloat.

package main

import (
    "fmt"
    "strconv"
)

func main() {
    numStr := "3.14159"
    
    // Using ParseFloat
    num1, err1 := strconv.ParseFloat(numStr, 64)
    if err1 != nil {
        fmt.Println("ParseFloat error:", err1)
    } else {
        fmt.Println("ParseFloat result:", num1)
    }
    
    // Using Sscanf
    var num2 float64
    _, err2 := fmt.Sscanf(numStr, "%f", &num2)
    if err2 != nil {
        fmt.Println("Sscanf error:", err2)
    } else {
        fmt.Println("Sscanf result:", num2)
    }
}

Sscanf is more flexible but slower than ParseFloat. Use ParseFloat for simple float conversions and Sscanf for more complex parsing needs.

Practical Example: Calculating Average

This practical example demonstrates using ParseFloat to calculate the average of numbers from command-line arguments.

package main

import (
    "fmt"
    "os"
    "strconv"
)

func main() {
    if len(os.Args) < 2 {
        fmt.Println("Please provide numbers to average")
        return
    }
    
    var sum float64
    count := len(os.Args[1:])
    
    for _, arg := range os.Args[1:] {
        num, err := strconv.ParseFloat(arg, 64)
        if err != nil {
            fmt.Printf("'%s' is not a valid number\n", arg)
            return
        }
        sum += num
    }
    
    average := sum / float64(count)
    fmt.Printf("Average: %.2f\n", average)
}

We iterate through command-line arguments, convert each to a float, and calculate the average. Invalid numbers terminate the program with an error.

Source

Go strconv package documentation

This tutorial covered the strconv.ParseFloat function in Go with practical examples of string-to-float conversion in various scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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