From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/c/variadic.html | 62 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 62 insertions(+) create mode 100644 devdocs/c/variadic.html (limited to 'devdocs/c/variadic.html') diff --git a/devdocs/c/variadic.html b/devdocs/c/variadic.html new file mode 100644 index 00000000..a824c453 --- /dev/null +++ b/devdocs/c/variadic.html @@ -0,0 +1,62 @@ +

Variadic functions

Variadic functions are functions (e.g. printf) which take a variable number of arguments.

+

The declaration of a variadic function uses an ellipsis as the last parameter, e.g. int printf(const char* format, ...);. See variadic arguments for additional detail on the syntax and automatic argument conversions.

+

Accessing the variadic arguments from the function body uses the following library facilities:

+ + + + + + + + +
Macros
Defined in header <stdarg.h>
enables access to variadic function arguments
(function macro)
accesses the next variadic function argument
(function macro)
+
(C99)
 makes a copy of the variadic function arguments
(function macro)
ends traversal of the variadic function arguments
(function macro)
Type
holds the information needed by va_start, va_arg, va_end, and va_copy
(typedef)

Example

+

Print values of different types.

+
#include <stdio.h>
+#include <stdarg.h>
+ 
+void simple_printf(const char* fmt, ...)
+{
+    va_list args;
+    va_start(args, fmt);
+ 
+    while (*fmt != '\0') {
+        if (*fmt == 'd') {
+            int i = va_arg(args, int);
+            printf("%d\n", i);
+        } else if (*fmt == 'c') {
+            // A 'char' variable will be promoted to 'int'
+            // A character literal in C is already 'int' by itself
+            int c = va_arg(args, int);
+            printf("%c\n", c);
+        } else if (*fmt == 'f') {
+            double d = va_arg(args, double);
+            printf("%f\n", d);
+        }
+        ++fmt;
+    }
+ 
+    va_end(args);
+}
+ 
+int main(void)
+{
+    simple_printf("dcff", 3, 'a', 1.999, 42.5); 
+}

Output:

+
3
+a
+1.999000
+42.50000

References

See also

+
C++ documentation for Variadic functions
+

+ © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
+ https://en.cppreference.com/w/c/variadic +

+
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