You can change the value of errno. Since errno is declared volatile , it might be changed asynchronously by a signal handler; see Defining Handlers. However, a properly written signal handler saves and restores the value of errno , so you generally do not need to worry about this possibility except when writing signal handlers. The initial value of errno at program startup is zero. In many cases, when a library function encounters an error, it will set errno to a non-zero value to indicate what specific error condition occurred.
The documentation for each function lists the error conditions that are possible for that function. So, instead, if you peek behind the curtain, you'll find that most implementations do something like. In this way, they can arrange for errno to work reasonably properly even in, say, multithreaded code. I assume you are using Linux, and I suppose that you don't directly use the system call, but some of the simple wrappers from your C library listed in syscalls 2.
Notice that some weird system calls are not wrapped by the C library a well known example of unwrapped system call would be sigreturn 2 which you probably should never use. Quite often the C library is GNU glibc , but it might be musl-libc etc. Notice also that kernel raw system calls have different calling conventions than ordinary C function so in practice a libc wrapper is required, and is in charge of dealing with errno.
Notice also that errno 3 is generally a macro almost behaving as some variable. Yes it is; you want to test errno only after some system call failure e.
Not any more. Please read carefully errno 3 documentation. BTW, SysV-style facilities tend to become obsolete and are not always available. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How to check the value of errno? Ask Question. Asked 4 years, 2 months ago.
Active 3 years, 9 months ago. Viewed 57k times. It is a common problem that at the time of dividing any number, programmers do not check if a divisor is zero and finally it creates a runtime error. C - Error Handling Advertisements. Previous Page. Next Page. Corrupted filesystem detected. Bad message. Invalid request descriptor. RPC struct is bad. Invalid request code. Invalid slot. Bad font-file format.
Device or resource is busy. Operation canceled. No child processes. Channel number is out of range. Communication error occurred on send. Software caused connection to abort. Connection refused. Connection reset by peer. Remap to the controlling terminal. Resource deadlock avoided. File locking deadlock. Destination address is required. Math argument is out of domain for the function. Disk quota exceeded. Endian not supported.
File exists. Bad address. File is too large. File positioning error. Host is down. Unable to communicate with remote node. Identifier removed. Illegal byte sequence. Operation now in progress. Interrupted function call. Invalid argument. Socket is already connected. Is a directory. Level 2 halted.
0コメント