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Table of Contents
Use the "comma ok" idiom
Example
Why this works
Common patterns
Home Backend Development Golang How to check if a key exists in a map in Go?

How to check if a key exists in a map in Go?

Jul 31, 2025 am 06:56 AM
go map

在Go中,使用“逗號ok”慣用法可以安全檢查鍵是否存在:1. 通過value, ok := myMap[key]獲取值和布爾標(biāo)志;2. ok為true表示鍵存在,false表示不存在;3. 若只關(guān)心存在性,可用_, ok := myMap[key];4. 結(jié)合delete函數(shù)可安全刪除存在的鍵。這種方法能準(zhǔn)確區(qū)分鍵不存在和值為零值的情況,是Go中檢查鍵存在的標(biāo)準(zhǔn)做法。

How to check if a key exists in a map in Go?

In Go, you can check if a key exists in a map using a simple and idiomatic syntax that takes advantage of Go's multiple return values from map lookups.

How to check if a key exists in a map in Go?

Use the "comma ok" idiom

When you access a key in a map, Go returns two values:

  • The value associated with the key (or the zero value if the key doesn't exist)
  • A boolean indicating whether the key was actually present

Here’s the syntax:

How to check if a key exists in a map in Go?
value, ok := myMap[key]
  • value is the value stored under key (or the zero value of the value type if the key doesn't exist)
  • ok is true if the key exists, false otherwise

Example

package main

import "fmt"

func main() {
    m := map[string]int{
        "apple": 5,
        "banana": 3,
    }

    // Check if key "apple" exists
    if value, ok := m["apple"]; ok {
        fmt.Printf("Found apple: %d\n", value)
    } else {
        fmt.Println("apple not found")
    }

    // Check if key "orange" exists
    if value, ok := m["orange"]; ok {
        fmt.Printf("Found orange: %d\n", value)
    } else {
        fmt.Println("orange not found") // This will print
    }
}

Why this works

Go maps return the zero value of the value type when a key doesn't exist. For example:

  • int → 0
  • string → ""
  • bool → false

So without checking ok, you can't distinguish between:

How to check if a key exists in a map in Go?
  • A key that doesn't exist
  • A key that exists but has a zero value

That’s why the ok boolean is essential for reliable existence checks.

Common patterns

  • Use _ if you only care about existence:
if _, ok := m["banana"]; ok {
    fmt.Println("banana exists")
}
  • Delete a key only if it exists:
if _, ok := m["apple"]; ok {
    delete(m, "apple")
}

Basically, just remember: value, ok := map[key] is the standard way to safely check for key existence in Go.

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