How to solve the 'panic: runtime error: slice bounds out of range' error in golang?

In the Go language, we often encounter an error, namely "panic: runtime error: slice bounds out of range" error. This is because when we use slices, we usually access or operate the slice, and the access index may go out of bounds. This article will explain the basic causes of this error, how to avoid and solve it.

1. Causes of slice out-of-bounds errors

Slice is a reference type, consisting of the underlying array, length and capacity. Normally, we access based on the length of the slice. If we exceed the length range of the slice, an error will be reported. Since the length of the underlying array is fixed, if we access an index position that is too long, the capacity of the underlying array will be exceeded, resulting in a "panic: runtime error: slice bounds out of range" error.

For example the following Go code:

func main() {
    nums := []int{1, 2, 3}
    fmt.Println(nums[3]) // 报错：panic: runtime error: index out of range
}

In the above code, we try to access the fourth element in the slice nums, but nums## The length of # is only 3, so it will cause "panic: runtime error: slice bounds out of range" error.

2. How to avoid slice out-of-bounds errors

In order to avoid slice out-of-bounds errors, we need to pay attention to the boundary conditions of the slice and ensure that our access and operations on the slice are within legal locations.

The following are some ways to avoid slice out-of-bounds errors:

2.1. Check the length of the slice

Normally, we need to ensure that our access to the slice is within the slice's length within the length range. If we need to increase or decrease the length of a slice, we need to be very careful and update the length of the slice in a timely manner.

For example, the following code shows how to use the

len function to get the length of a slice and loop through all slice elements:

func main() {
    nums := []int{1, 2, 3}
    for i := 0; i < len(nums); i++ {
        fmt.Println(nums[i])
    }
}

2.2. Using the slice operator

There is a special slice operator in the Go language that can help us avoid slice out-of-bounds errors. The syntax of the slice operator is

a[low:high], where low and high are the lower and upper bounds of the slice respectively. When using the slice operator, we only need to ensure that the upper bound is not greater than the length of the slice to avoid slice out-of-bounds errors.

For example, the following code shows how to use the slice operator to obtain a subrange of a slice:

func main() {
    nums := []int{1, 2, 3, 4, 5}
    subnums := nums[1:3] // 获取 nums[1], nums[2]
    for i := 0; i < len(subnums); i++ {
        fmt.Println(subnums[i])
    }
}

2.3. Avoid index out-of-bounds

When using an index to access a subrange of a slice element, we need to ensure that the index position is within the length range of the slice, otherwise it will cause a slice out-of-bounds error. In order to avoid the problem of index out-of-bounds, we can use the

range keyword to loop through the elements in the slice, so that we do not need to manually handle the index position.

For example, the following code shows how to use

range to loop through all elements in a slice:

func main() {
    nums := []int{1, 2, 3}
    for _, num := range nums {
        fmt.Println(num)
    }
}

3. How to resolve slice out-of-bounds errors

If we accidentally encounter an out-of-bounds slice error while writing Go code, we need to know how to find and resolve this error.

The following are some ways to solve slice out-of-bounds errors:

3.1. Use debugging tools

When we write complex Go code, some difficult-to-debug problems may occur. question. To solve these problems, we can use debugging tools to help us diagnose runtime errors in our programs.

Commonly used debugging tools include

gdb, delve, etc. These tools can help us pause the execution of the program so that we can examine the variables, stack, and other information in the program.

3.2. Add error checking

In order to avoid slice out-of-bounds errors, we need to ensure that our access and operation of slices are within the legal range. If we use an index when looping through a slice and do not perform out-of-bounds checking, an error will occur in the program.

To avoid this situation, we can add some error checking code. For example, we can use the

len function to check the length of the slice, then manually calculate where the loop traversal should end, and add an out-of-bounds check within the loop body.

The following is a sample code:

func main() {
    nums := []int{1, 2, 3}
    for i := 0; i < len(nums); i++ {
        if i >= len(nums) {
            fmt.Println("越界啦")
            break
        }
        fmt.Println(nums[i])
    }
}

3.3. Using Go’s built-in functions

In addition to the above methods, the Go language also provides some built-in functions to help us avoid slicing out of bounds mistake. For example, the

copy function can use a copy between slices to ensure that it does not go out of bounds:

func main() {
    nums := []int{1, 2, 3}
    copynums := make([]int, len(nums))
    copy(copynums, nums)
}

Summary

The slice out-of-bounds error is one of the common errors in the Go language, usually Appears when we use slice access or operations. In order to avoid this error, we need to pay attention to the boundary conditions of slices and ensure that our access and operations on slices are within legal locations. If we encounter a slice out-of-bounds error, we can use debugging tools to diagnose, or add some error checking or use Go's built-in functions to avoid out-of-bounds.

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