Always check the return value to see if the function succeeded before you do any further operations on the file. If an error occurs, the error code is returned and the global variable `errno` is set. For more information, see [`errno`, `_doserrno`, `_sys_errlist`, and `_sys_nerr`](../errno-doserrno-sys-errlist-and-sys-nerr.md).

Always check the return value to see whether the pointer is NULL before you perform any other operations on the file. If an error occurs, the global variable `errno` is set and may be used to obtain specific error information. For more information, see [`errno`, `_doserrno`, `_sys_errlist`, and `_sys_nerr`](../errno-doserrno-sys-errlist-and-sys-nerr.md).

The **`_fpclass`** and **`_fpclassf`** functions are Microsoft-specific. They are similar to [`fpclassify`](fpclassify.md), but return more detailed information about the argument. The **`_fpclassf`** function is only available when compiled for the x64 platform.

|`Operand1`<br/>`Operand2`<br/>`Result`|These `_FPIEEE_VALUE` structures indicate the types and values of the proposed result and operands. Each structure contains these fields:<br /><br /> `OperandValid` - Flag indicating whether the responding value is valid.<br />`Format` - Data type of the corresponding value. The format type might be returned even if the corresponding value is not valid.<br />`Value` - Result or operand data value.|

|`Cause`<br/>`Enable`<br/>`Status`|`_FPIEEE_EXCEPTION_FLAGS` contains one bit field per type of floating point exception. There is a correspondence between these fields and the arguments used to mask the exceptions supplied to [`_controlfp`](control87-controlfp-control87-2.md). The exact meaning of each bit depends on context:<br /><br /> `Cause` - Each set bit indicates the particular exception that was raised.<br />`Enable` - Each set bit indicates that the particular exception is currently unmasked.<br />`Status` - Each set bit indicates that the particular exception is currently pending. This includes exceptions that have not been raised because they were masked by `_controlfp`.|

Pending exceptions that are disabled are raised when you enable them. This can result in undefined behavior when using **`_fpieee_flt`** as an exception filter. Always call [`_clearfp`](clear87-clearfp.md) before enabling floating point exceptions.

**`_fprintf_p`** formats and prints a series of characters and values to the output *`stream`*. Each function *`argument`* (if any) is converted and output according to the corresponding format specification in *`format`*. For **`_fprintf_p`**, the *`format`* argument has the same syntax and use that it has in `_printf_p`. These functions support positional parameters, meaning that the order of the parameters used by the format string can be changed. For more information about positional parameters, see [printf_p Positional Parameters](../printf-p-positional-parameters.md).

**`_fputc_nolock`** and **`_fputwc_nolock`** are identical to `fputc` and `fputwc`, respectively, except that they are not protected from interference by other threads. They might be faster because they do not incur the overhead of locking out other threads. Use these functions only in thread-safe contexts such as single-threaded applications or where the calling scope already handles thread isolation.

The two functions behave identically if the stream is opened in ANSI mode. **`_fputc_nolock`** does not currently support output into a UNICODE stream.

The console is not supported in Universal Windows Platform (UWP) apps. The standard stream handles that are associated with the console—`stdin`, `stdout`, and `stderr`—must be redirected before C run-time functions can use them in UWP apps. For more compatibility information, see [Compatibility](../compatibility.md).

Each of these functions returns the character written. For **`_fputchar`**, a return value of `EOF` indicates an error. For **`_fputwchar`**, a return value of `WEOF` indicates an error. If c is `NULL`, these functions generate an invalid parameter exception, as described in [Parameter validation](../parameter-validation.md). If execution is allowed to continue, they return `EOF` (or `WEOF`) and set `errno` to `EINVAL`.

Both of these functions writes the single character *`c`* to `stdout` and advances the indicator as appropriate. **`_fputchar`** is equivalent to `fputc( stdout )`. It is also equivalent to `putchar`, but implemented only as a function, rather than as a function and a macro. Unlike `fputc` and `putchar`, these functions are not compatible with the ANSI standard.

The console is not supported in Universal Windows Platform (UWP) apps. The standard stream handles that are associated with the console—`stdin`, `stdout`, and `stderr`—must be redirected before C run-time functions can use them in UWP apps. For more compatibility information, see [Compatibility](../compatibility.md).