C++17引入了std::filesystem库 (文件系统库, filesystem library)。这里整理下std::filesystem::directory_entry的使用。
std::filesystem::directory_entry，目录项，获取文件属性 。此directory_entry类主要用法包括：
(1).构造函数、operator=、assign：赋值；
(2).replace_filename: 更改目录项的文件名；
(3).path: 返回std::filesystem::path对象；
(4).exists: 检查指定的目录项是否存在 ；
(5).is_block_file、is_character_file: 检查目录项是否是块设备(block device)、字符设备(character device)；
(6).is_directory: 检查目录项是否是目录；
(7).is_fifo: 检查目录项是否是命令管道；
(8).is_other: 检查目录项是否是其它文件(不是常规文件、目录或符号链接)；
(9).is_regular_file: 检查目录项是否是常规文件；
(10).is_socket: 检查目录项是否是命名套接字；
(11).is_symlink: 检查目录项是否是符号链接；
(12).file_size: 获取目录项指定的文件大小 ；
(13).last_write_time:获取目录项最后修改时间。
以下为测试代码：注意windows和linux结果输出的差异
cpp
namespace {
float get_file_size(std::uintmax_t size, std::string& suffix)
{
float s1 = size / 1024. / 1024 / 1024;
float s2 = size / 1024. / 1024;
float s3 = size / 1024.;
if (s1 > 1) {
suffix = " GB";
return s1;
}
if (s2 > 1) {
suffix = " MB";
return s2;
}
if (s3 > 1) {
suffix = " KB";
return s3;
}
suffix = " Bytes";
return size;
}
std::string to_time_t(std::filesystem::file_time_type tp)
{
using namespace std::chrono;
auto sctp = time_point_cast<system_clock::duration>(tp - std::filesystem::file_time_type::clock::now() + system_clock::now());
auto tt = system_clock::to_time_t(sctp);
std::tm* gmt = std::localtime(&tt); // UTC: std::gmtime(&tt);
std::stringstream buffer;
buffer << std::put_time(gmt, "%Y-%m-%d %H:%M:%S");
return buffer.str();
}
} // namespace
int test_filesystem_directory_entry()
{
namespace fs = std::filesystem;
// 1. construct,operator=,assign
fs::directory_entry d1{ fs::current_path() };
fs::directory_entry d2 = d1;
fs::directory_entry d3;
d3.assign(fs::current_path());
if ((d1 == d2) && (d1 == d3))
std::cout << "they are equal" << std::endl; // they are equal
// windows: d1:"E:\\GitCode\\Messy_Test\\prj\\x86_x64_vc12\\CppBaseTest"
// linux: d1:"/home/spring/GitCode/Messy_Test/prj/linux_cmake_CppBaseTest"
std::cout << "d1:" << d1 << std::endl;
// 2. replace_filename
d1.replace_filename("C++17Test");
// windows: d1:"E:\\GitCode\\Messy_Test\\prj\\x86_x64_vc12\\C++17Test"
// linux: d1:"/home/spring/GitCode/Messy_Test/prj/C++17Test"
std::cout << "d1:" << d1 << std::endl;
// 3. path
fs::path p1 = d1.path();
// windows: p1:"E:\\GitCode\\Messy_Test\\prj\\x86_x64_vc12\\C++17Test"
// linux: p1:"/home/spring/GitCode/Messy_Test/prj/C++17Test"
std::cout << "p1:" << p1 << std::endl;
// 4. exists
for (const auto& str : { "C:\\Program Files (x86)", "/usr/local" , "E:\\GitCode\\xxx", "/usr/xxx"}) {
fs::directory_entry entry{ str };
/* windows:
directory entry: "C:\\Program Files (x86)":exists
directory entry: "/usr/local":does not exist
directory entry: "E:\\GitCode\\xxx":does not exist
directory entry: "/usr/xxx":does not exist */
/* linux:
directory entry: "C:\\Program Files (x86)":does not exist
directory entry: "/usr/local":exists
directory entry: "E:\\GitCode\\xxx":does not exist
directory entry: "/usr/xxx":does not exist
*/
std::cout << "directory entry: " << entry << (entry.exists() ? ":exists\n" : ":does not exist\n");
}
// 5. is_block_file,is_character_file,is_directory,is_fifo,is_other,is_regular_file,is_socket,is_symlink
for (const auto& str : { "/dev/null", "C:\\Program Files (x86)", "/usr/include/time.h", "C:\\MinGW\\bin\\c++filt.exe",
"/usr/bin/g++", "/dev/block/11:0"}) {
fs::directory_entry entry{ str };
/* windows:
"C:\\Program Files (x86)" is a directory
"C:\\MinGW\\bin\\c++filt.exe" is a regular_file */
/* linux:
"/dev/null" is a character device
"/dev/null" is an other file
"/usr/include/time.h" is a regular_file
"/usr/bin/g++" is a regular_file
"/usr/bin/g++" is a symlink
"/dev/block/11:0" is a block device
"/dev/block/11:0" is an other file
"/dev/block/11:0" is a symlink */
if (entry.is_block_file())
std::cout << entry << " is a block device" << std::endl;
if (entry.is_character_file())
std::cout << entry << " is a character device" << std::endl;
if (entry.is_directory())
std::cout << entry << " is a directory" << std::endl;
if (entry.is_fifo())
std::cout << entry << " is a FIFO" << std::endl;
if (entry.is_other())
std::cout << entry << " is an other file" << std::endl;
if (entry.is_regular_file())
std::cout << entry << " is a regular_file" << std::endl;
if (entry.is_socket())
std::cout << entry << " is a named socket" << std::endl;
if (entry.is_symlink())
std::cout << entry << " is a symlink" << std::endl;
}
// 6. file_size, last_write_time
for (const auto& str : { "/usr/bin/g++", "D:\\FSCapture.exe", "D:\\DownLoad\\tmp.txt", "/usr/bin/cmake", "E:\\yulong.mp4"}) {
fs::directory_entry entry{ str };
/* windows:
"D:\\FSCapture.exe" size: 2.82 MB
"D:\\FSCapture.exe" last write time: 2016-03-29 09:26:26
"D:\\DownLoad\\tmp.txt" size: 10 Bytes
"D:\\DownLoad\\tmp.txt" last write time: 2023-09-26 09:00:35
"E:\\yulong.mp4" size: 1.35 GB
"E:\\yulong.mp4" last write time: 2023-08-19 22:42:56 */
/* linux:
"/usr/bin/g++" size: 910.82 KB
"/usr/bin/g++" last write time: 2023-05-13 15:52:47
"/usr/bin/cmake" size: 6.43 MB
"/usr/bin/cmake" last write time: 2022-08-17 18:44:05 */
if (entry.is_regular_file()) {
std::string suffix;
auto value = get_file_size(entry.file_size(), suffix);
if (suffix == " Bytes")
std::cout << entry << " size: " << static_cast<int>(value) << suffix << std::endl;
else
std::cout << entry << " size: " << std::fixed << std::setprecision(2) << value << suffix << std::endl;
std::cout << entry << " last write time: " << to_time_t(entry.last_write_time()) << std::endl;
}
}
return 0;
}执行结果如下图所示：
