Read bytes from file, save them to structure and modify values
php editor Youzi will introduce you to a common operation, which is to read bytes from a file and save them into a structure. You can also modify the structure. value. This kind of operation is very common in programming, especially when dealing with binary files or network data. By reading bytes and saving them into a structure, we can easily access and modify the data in the file, thereby achieving flexible processing of the file. Next, we will explain in detail how to implement this process, hoping to help everyone.
Question content
I am new to Go. I looked at the Coursera introduction to the Go language, but some topics were not discussed in depth.
To practice Go, I'm solving as many exercises in CS50 as I can. I'm working on an example right now where I need to read a bmp file, copy the header content into a corresponding data structure, change some parameters in that structure and then copy the result into a new file.
The first thing I noticed was that I couldn't read in binary the number of bytes corresponding to the size of the structure I created. This is due to padding that may occur when building the structure. I am able to read and populate the structure field by field.
To improve this, I tried iterating the structure, getting the size of each field, reading the corresponding number of bytes from the file, and then writing to the file again after iterating the structure. p>
I'm stuck on the last step (if the previous steps were done correctly): how to set the value correctly based on the field type?
package main import ( "bufio" "encoding/binary" "fmt" "os" "reflect" ) type DWORD uint32 type WORD uint16 type BITMAPFILEHEADER struct { BfType WORD BfSize DWORD BfReserved1 WORD BfReserved2 WORD BfOffBits DWORD } func main() { input_file, err := os.Open("harvard_bottomup.bmp") if err != nil { fmt.Println("Could not open the origin file.") fmt.Println(err) } var bf BITMAPFILEHEADER reader := bufio.NewReader(input_file) value := reflect.ValueOf(&bf).Elem() n := value.NumField() structType := value.Type() for i := 0; i < n; i++ { b := make([]byte, structType.Field(i).Type.Size()) err = binary.Read(reader, binary.BigEndian, b) if err != nil { fmt.Println(err) } fmt.Printf("Field Name: %-15s %-15s %02x\n", structType.Field(i).Name, structType.Field(i).Type, b) // I should now set the value, but I don't know how to switch between types // value.Field(i).Set... } input_file.Close() }
PS: Before this, I tried to read the fields in the structure directly, but I couldn't do it.
Workaround
Looks like you are duplicating the functionality in the binary.Read function. This function decodes data in the specified byte order into contiguous fields in a structure. You can view the structure decoding code here< /a>.
Here's how to use Read to decode the file header:
input_file, err := os.Open("harvard_bottomup.bmp") if err != nil { fmt.Println("Could not open the origin file.") fmt.Println(err) return } defer input_file.Close() reader := bufio.NewReader(input_file) var bf BITMAPFILEHEADER err = binary.Read(reader, binary.BigEndian, &bf) if err != nil { fmt.Println(err) return }
The above is the detailed content of Read bytes from file, save them to structure and modify values. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics





OpenSSL, as an open source library widely used in secure communications, provides encryption algorithms, keys and certificate management functions. However, there are some known security vulnerabilities in its historical version, some of which are extremely harmful. This article will focus on common vulnerabilities and response measures for OpenSSL in Debian systems. DebianOpenSSL known vulnerabilities: OpenSSL has experienced several serious vulnerabilities, such as: Heart Bleeding Vulnerability (CVE-2014-0160): This vulnerability affects OpenSSL 1.0.1 to 1.0.1f and 1.0.2 to 1.0.2 beta versions. An attacker can use this vulnerability to unauthorized read sensitive information on the server, including encryption keys, etc.

Queue threading problem in Go crawler Colly explores the problem of using the Colly crawler library in Go language, developers often encounter problems with threads and request queues. �...

The library used for floating-point number operation in Go language introduces how to ensure the accuracy is...

Backend learning path: The exploration journey from front-end to back-end As a back-end beginner who transforms from front-end development, you already have the foundation of nodejs,...

The difference between string printing in Go language: The difference in the effect of using Println and string() functions is in Go...

This article introduces a variety of methods and tools to monitor PostgreSQL databases under the Debian system, helping you to fully grasp database performance monitoring. 1. Use PostgreSQL to build-in monitoring view PostgreSQL itself provides multiple views for monitoring database activities: pg_stat_activity: displays database activities in real time, including connections, queries, transactions and other information. pg_stat_replication: Monitors replication status, especially suitable for stream replication clusters. pg_stat_database: Provides database statistics, such as database size, transaction commit/rollback times and other key indicators. 2. Use log analysis tool pgBadg

The problem of using RedisStream to implement message queues in Go language is using Go language and Redis...

Under the BeegoORM framework, how to specify the database associated with the model? Many Beego projects require multiple databases to be operated simultaneously. When using Beego...
