The **`errno`** values are constants assigned to [`errno`](../c-runtime-library/errno-doserrno-sys-errlist-and-sys-nerr.md) in the event of various error conditions.

The **`errno`** values in a 32-bit Windows operating system are a subset of the values for **`errno`** in XENIX systems. Thus, the **`errno`** value is not necessarily the same as the actual error code returned by a system call from the Windows operating systems. To access the actual operating system error code, use the [`_doserrno`](../c-runtime-library/errno-doserrno-sys-errlist-and-sys-nerr.md) variable, which contains this value.

|**`EDEADLOCK`**|Resource deadlock would occur. The argument to a math function is not in the domain of the function.|

|**`EDOM`**|Math argument.|

|**`EEXIST`**|Files exist. An attempt has been made to create a file that already exists. For example, the **`_O_CREAT`** and **`_O_EXCL`** flags are specified in an **`_open`** call, but the named file already exists.|

|**`EINVAL`**|Invalid argument. An invalid value was given for one of the arguments to a function. For example, the value given for the origin when positioning a file pointer (by means of a call to **`fseek`**) is before the beginning of the file.|

|**`EMFILE`**|Too many open files. No more file descriptors are available, so no more files can be opened.|

|**`ENOENT`**|No such file or directory. The specified file or directory does not exist or cannot be found. This message can occur whenever a specified file does not exist or a component of a path does not specify an existing directory.|