# FileSystemManager.ftruncate(Object object)

Start from base library version 2.16.1. Please remaining backward compatible.

with Promise style call: Not supported

Mini Program plugin: Support, need to Mini Program base library version no less than 2.19.2

Truncate file contents

# parameter

# Object object

attribute	type	Required	Introductions
fd	string	yes	File descriptor. fd adopt FileSystemManager.open or FileSystemManager.openSync Interface acquisition
length	number	yes	Truncate position, default 0. if length Is less than the file length in bytes, only the first length Four bytes will remain in the file and the rest will be deletedif length Is greater than the file length, it will be expanded, and the extension will be filled with empty bytes0'）
success	function	no	Interface calls the successful callback function
fail	function	no	Interface calls failed callback functions
complete	function	no	Callback function at the end of an interface call (both successful and unsuccessful calls are executed)

# object.fail callback

# parameter

# Object res

attribute	type	Introductions
errMsg	string	Error message

res.errMsg Legal value

value	Introductions	Minimum version
bad file descriptor	Invalid file descriptor
fail permission denied	Specified fd No write permissions
fail the maximum size of the file storage limit is exceeded	Insufficient storage space
fail sdcard not mounted	android sdcard Mount failure

# sample code

const fs = wx.getFileSystemManager()
// Open the file
fs.open({
  filePath: `${wx.env.USER_DATA_PATH}/hello.txt`, 
  flag: 'a+',
  success(res) {
    // Truncate file contents
    fs.ftruncate({
      fd: res.fd,
      length: 10, // Truncate the file from the 10th byte
      success(res) {
        console.log(res)
      }
    })
  }
})