What is Vfprintf?

What is Vfprintf?

The vfprintf() function writes a formatted string to a specified output stream (example: file or database). Unlike fprintf(), the arguments in vfprintf(), are placed in an array. This function works “step-by-step”.

Where is Vsnprintf defined?

vsnprintf() prototype int vsnprintf( char* buffer, size_t buf_size, const char* format, va_list vlist ); The string format may contain format specifiers starting with % which are replaced by the values of variables that are passed as a list vlist . It is defined in header file.

Is Vfprintf thread safe?

1 Answer. Anyways, vprintf() is a thread-safe function but it has a limitation that a read immediately following a write or a write immediately following a read there must be a flush work be done. May be flushing it could solve the problem for you.

What is va_list in C?

va_list is a complete object type suitable for holding the information needed by the macros va_start, va_copy, va_arg, and va_end. It is legal to pass a pointer to a va_list object to another function and then use that object after the function returns.

What does Vsprintf do in C?

C Language: vsprintf function. (Formatted String Write Using Variable Argument List) In the C Programming Language, the vsprintf function writes formatted output to an object pointed to by s using arg as the variable argument list.

How do I format a string in C++?

The sprintf() function in C++ is used to write a formatted string to character string buffer….Commonly Used Format Specifiers.

What is Va_start?

The va_start macro enables access to the variable arguments following the named argument parm_n . va_start should be invoked with an instance to a valid va_list object ap before any calls to va_arg.

Where is Va_start defined?

The C standard macros, defined in STDARG. H , are used as follows: va_start sets arg_ptr to the first optional argument in the list of arguments that’s passed to the function.

Is Va list thread safe?

Each thread invoking your function will gets its own copy of that va_list iterating over its own stack. There will be no conflict between the threads. Yes, two calls of va_start on a single va_list would invalidate that list.

What is Va_start and Va_end?

The va_arg(), va_end(), and va_start() macros access the arguments to a function when it takes a fixed number of required arguments and a variable number of optional arguments. Corresponding va_start() and va_end() macro calls must be in the same function.

How does va_list work in C?

In the most usual stack-based situation, the va_list is merely a pointer to the arguments sitting on the stack, and va_arg increments the pointer, casts it and dereferences it to a value. Then va_start initialises that pointer by some simple arithmetic (and inside knowledge) and va_end does nothing.

How do I use Vsprintf?

A precision of 0 means that no character is written for the value 0. For e, E and f specifiers − this is the number of digits to be printed after the decimal point….Parameters.

What does vfprintf do in C?

C library function – vfprintf() Description. The C library function int vfprintf(FILE *stream, const char *format, va_list arg) sends formatted output to a stream using an argument list passed to it.

What is the return value of vfwprintf?

vfprintf and vfwprintf return the number of characters written, not including the terminating null character, or a negative value if an output error occurs. If either stream or format is a null pointer, the invalid parameter handler is invoked, as described in Parameter Validation.

What is%n in printf_s?

The memory-writing conversion specifier %n is a common target of security exploits where format strings depend on user input and is not supported by the bounds-checked printf_s family of functions.

What is the difference between printf and Arg?

C string that contains a format string that follows the same specifications as formatin printf(see printffor details). arg A value identifying a variable arguments list initialized with va_start.