On Linux I open a file with the following code:
auto file = ::open("file.dat", O_RDWR | O_CREAT);
but when I try to compile this code for Android (android-ndk-r26-beta2) I get the following compiler error:
error: 'open' called with O_CREAT or O_TMPFILE, but missing mode
what value should I pass to make it compile? Where is the documentation?
As far as I see it is bionic. What is its status?
It should be something like:
auto file = ::open("file.dat", O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
see https://codeql.github.com/codeql-query-help/cpp/cpp-open-call-with-mode-argument/
If you use O_CREAT variant, this is because you want the file to be created if non existing yet. Thus, in the case of creation it is requested that the file have permission bits set to some value (read, write, execute, etc). This is documented in man page of open:
O_CREAT[...]
The mode argument specifies the file mode bits to be applied when a new file is created. If neither O_CREAT nor O_TMPFILE is specified in flags, then mode is ignored (and can thus be specified as 0, or simply omitted). The mode argument must be supplied if O_CREAT or O_TMPFILE is specified in flags; if it is not supplied, some arbitrary bytes from the stack will be applied as the file mode.
The effective mode is modified by the process's umask in the usual way: in the absence of a default ACL, the mode of the created file is (mode & ~umask).
Note that mode applies only to future accesses of the newly created file; the open() call that creates a read- only file may well return a read/write file descriptor.
The following symbolic constants are provided for mode:
S_IRWXU 00700 user (file owner) has read, write, and execute permission S_IRUSR 00400 user has read permission S_IWUSR 00200 user has write permission S_IXUSR 00100 user has execute permission S_IRWXG 00070 group has read, write, and execute permission S_IRGRP 00040 group has read permission S_IWGRP 00020 group has write permission S_IXGRP 00010 group has execute permission S_IRWXO 00007 others have read, write, and execute permission S_IROTH 00004 others have read permission S_IWOTH 00002 others have write permission S_IXOTH 00001 others have execute permission According to POSIX, the effect when other bits are set in mode is unspecified. On Linux, the following bits are also honored in mode: S_ISUID 0004000 set-user-ID bit S_ISGID 0002000 set-group-ID bit (see inode(7)). S_ISVTX 0001000 sticky bit (see inode(7)). [...]
You have to make a call like:
auto file = ::open("file.dat", O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
or something like that.
