NAME

gnu::format - specify the style of format string

SYNOPSIS

[[gnu::format(style, fmt-idx, first-idx)]]

DESCRIPTION

This attribute can be applied to a function. It specifies that a function parameter is a format string, and specifies the style of the format string. This allows checking the syntax of the format string, as well as the types of the variadic arguments. The style can be one of the following.

printf

scanf

strftime

strfmon

fmt-idx is a 1-based index that specifies the position of the format string within the parameter list.

first-idx is a 1-based index that specifies the position of the first argument that corresponds to the format string. If the first argument is part of a va_list argument, it should be specified as 0.

VERSIONS

STANDARDS

GNU.

HISTORY

gcc, g++, clang 2.8, clang++ 2.8.

EXAMPLES

[[gnu::format(printf, 3, 0)]]
int
vstprintf(int size;
    char buf[restrict size], int size,
    const char *restrict fmt, va_list args)
{
	int len;
	if (size == 0) {
		errno = EOVERFLOW;
		return -1;
	}
	len = vsnprintf(buf, size, fmt, args);
	if (len >= size) {
		errno = E2BIG;
		return -1;
	}
	return len;
}
[[gnu::format(printf, 3, 4)]]
int
stprintf(int size;
    char buf[restrict size], int size,
    const char *restrict fmt, ...)
{
	int len;
	va_list args;
	va_start(args, fmt);
	len = vstprintf(buf, size, fmt, args);
	va_end(args);
	return len;
}