# 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 Default values 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
  filePath: `${wx.env.USER_DATA_PATH}/hello.txt`, 
  flag: 'a+',
  success(res) {
    // Truncate file contents
      fd: res.fd,
      length: 10, // Truncate the file from the 10th byte
      success(res) {