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I. conversion between types

Data types in C language can be converted

Forced type conversion

Implicit type conversion

II. Mandatory type conversion

Syntax for casting

(Type) var_name

(Type) value

The result of a cast

The target type can accommodate the target value: the result remains the same

The target type cannot hold the target value: the result will be truncated

Note: not all casts are successful, and when casts cannot be performed, the compiler will generate error messages (such as converting custom data types to basic data types).

Let's take a look at a piece of code that enforces a cast:

# include struct TS {int i; int j;}; struct TS ts; int main () {short s = 0x1122; char c = (char) s; / / 0x22 int I = (int) s; / / 0x00001122 int j = (int) 3.1415; / / 3 unsigned int p = (unsigned int) & ts; / / long l = (long) ts; / / error / / ts = (struct TS) l / / error printf ("s =% x\ n", s); printf ("c =% x\ n", c); printf ("I =% x\ n", I); printf ("j =% x\ n", j); printf ("p =% x\ n", p); printf ("& ts =% p\ n", & ts); return 0;}

The following is the output:

Note that converting custom data types to basic data types will result in an error.

III. Implicit type conversion

Implicit type conversion is a type conversion actively performed by the compiler.

Note:

Implicit type conversion from low type to high type is safe and does not produce truncation.

Implicit type conversion from high type to low type is unsafe and leads to incorrect results

Implicit type conversion in expressions

The occurrence point of implicit type conversion

In arithmetic expressions, low types are converted to high types

In an assignment expression, the value of the expression is converted to the type of the variable on the left

When a function is called, the argument is converted to the type of formal parameter

Function returns a value, and the return expression is converted to the return value type

Secure implicit type conversion:

Let's take a look at an implicit type conversion code:

# include int main () {char c = 'a'; int i = c; / safe unsigned int j = 0x11223344; short s = j; / unsafe printf ("c =% c\ n", c); printf ("I =% d\ n", I); printf ("j =% x\ n", j); printf ("s =% x\ n", s) Printf ("sizeof (c + s) =% d\ n", sizeof (c + s)); return 0;}

The following is the output:

C is char type, s is short type. Before the four operations, each addition narrower than int is automatically raised to int, and the result is also int type, so size is 4.

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