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/language%2Fcast.html | 64 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) create mode 100644 devdocs/c/language%2Fcast.html (limited to 'devdocs/c/language%2Fcast.html') diff --git a/devdocs/c/language%2Fcast.html b/devdocs/c/language%2Fcast.html new file mode 100644 index 00000000..aae5fe1a --- /dev/null +++ b/devdocs/c/language%2Fcast.html @@ -0,0 +1,64 @@ +

cast operator

Performs explicit type conversion

+

Syntax

+ +
( type-name ) expression

where

+ + + +
type-name - either the type void or any scalar type
expression - any expression of scalar type (unless type-name is void, in which case it can be anything)

Explanation

If type-name is void, then expression is evaluated for its side-effects and its returned value is discarded, same as when expression is used on its own, as an expression statement.

+

Otherwise, if type-name is exactly the type of expression, nothing is done (except that if expression has floating type and is represented with greater range and precision than its type indicates -- see below)

+

Otherwise, the value of expression is converted to the type named by type-name, as follows:

+

Every implicit conversion as if by assignment is allowed.

+

In addition to the implicit conversions, the following conversions are allowed:

+

In any case (both when executing an implicit conversion and in the same-type cast), if expression and type-name are floating types and expression is represented with greater range and precision than its type indicates (see FLT_EVAL_METHOD), the range and precision are stripped off to match the target type.

+

The value category of the cast expression is always non-lvalue.

+

Notes

Because const, volatile, restrict, and _Atomic qualifiers have effect on lvalues only, a cast to a cvr-qualified or atomic type is exactly equivalent to the cast to the corresponding unqualified type.

+

The cast to void is sometimes useful to silence compiler warnings about unused results.

+

The conversions not listed here are not allowed. In particular,

+ + +

If the implementation provides intptr_t and/or uintptr_t, then a cast from a pointer to an object type (including cv void) to these types is always well-defined. However, this is not guaranteed for a function pointer.

+		 (since C99)

Note that conversions between function pointers and object pointers are accepted as extensions by many compilers, and expected by some usages of POSIX dlsym() function.

+

Example

#include <stdio.h>
+ 
+int main(void)
+{
+    // examining object representation is a legitimate use of cast
+    double d = 3.14;
+    printf("The double %.2f (%a) is: ", d, d);
+    for (size_t n = 0; n < sizeof d; ++n)
+        printf("0x%02x ", ((unsigned char*)&d)[n]);
+ 
+    // edge cases
+    struct S { int x; } s;
+//    (struct S)s; // error; not a scalar type
+                   // even though casting to the same type does nothing
+    (void)s; // okay to cast any type to void
+}

Possible output:

+
The double 3.14 (0x1.91eb851eb851fp+1) is: 0x1f 0x85 0xeb 0x51 0xb8 0x1e 0x09 0x40

References

See also

+
C++ documentation for explicit type conversion
+

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

+
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