Embed Size (px)
Citation preview
Young Won Lim2/17/18
Type Cast (1A)
Young Won Lim2/17/18
Copyright (c) 2010-2018 Young W. Lim.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".
Please send corrections (or suggestions) to [email protected].
This document was produced by using LibreOffice.
Type Cast 3 Young Won Lim2/17/18
Type Conversion
Implicit Type Conversion
m = (int) 1.25;
Explicit Type Conversion
Promotion
Demotion
1 / 2.0 1.0 / 2.0
int m;m = 1.25; m = 1; truncation problem
No warning message
Type Cast 4 Young Won Lim2/17/18
0 0 0 0
Type Conversion (int → double) – implicit one
Implicit Type Conversion Promotion
int m;m = 123;
double x;x = m;
0x7B
0 1 1 1 1 0 1 1
0 1 1 1 1 0 1 1
1 1 1 0 1 1 0 0
(0x7B / 2^6) * 2^6
implicit one
0 0 0 0
0 0
0xEC 00 00 00 …
Type Cast 5 Young Won Lim2/17/18
Type Conversion (int → double) – 16 hexa digits
Exponent : 11bitSign : 1bit = 4 * 3 → 3 hexa digits
6+ 1023 = 1029 → 0x405
0x405 EC 00 00 00 00 00 0
(0x7B / 2^6) * 2^6
0xEC 00 00 00 00 00 0
Fraction : 52bit = 4 * 13 → 13 hexa digits
excess 1023 code
0x40 5E C0 00 00 00 00 00
Type Cast 6 Young Won Lim2/17/18
Type Conversion (int → double) – Little Endian
0x40 5E C0 00 00 00 00 00
LSBMSB
00
00
00
00
00
C0
5E
40
0x0000
0x0001
0x0002
0x0003
0x0004
0x0005
0x0006
0x0007 MSB
LSB
1-byte
Little Endian:LSByte First
Type Cast 7 Young Won Lim2/17/18
Type Casting
double x = 123;int *p;double *q;
00
00
00
00
00
C0
5E
40
0x0000
0x0001
0x0002
0x0003
0x0004
0x0005
0x0006
0x0007
0x0008
0x0009
0x000A
0x000B
0x000C
0x000D
0x000E
0x000F
p q
Type Cast 8 Young Won Lim2/17/18
Type Casting
double x = 123;int *p;double *q;
q = &x;
00
00
00
00
00
C0
5E
40
0x0000
0x0001
0x0002
0x0003
0x0004
0x0005
0x0006
0x0007
0x0008
0x0009
0x000A
0x000B
0x000C
0x000D
0x000E
0x000F
q
*q → 123.0
Type Cast 9 Young Won Lim2/17/18
Type Casting
double x = 123;int *p;double *q;
p = (int *) &x;
00
00
00
00
00
C0
5E
40
0x0000
0x0001
0x0002
0x0003
0x0004
0x0005
0x0006
0x0007
0x0008
0x0009
0x000A
0x000B
0x000C
0x000D
0x000E
0x000F
p
*p → 0
Series:2. Pointers
10 Young Won Lim2/17/18
Pointer Type Cast
Series:2. Pointers
11 Young Won Lim2/17/18
Changing the associated data type of an address
long a;
int * p;
short * q;
char * r;
address of a long value
address of an int value
address of a short value
address of a char value
Series:2. Pointers
12 Young Won Lim2/17/18
Pointer Type Casting
long a;
int * p;
short * q;
char * r;
&a
q = (short *) &a
r = (char *) &a
p = (int *) &a
address of a long value
address of an int value
address of a short value
address of a char value
Series:2. Pointers
13 Young Won Lim2/17/18
Re-interpretation of memory data – case I
long a;
int *p;
short *q;
char *r; 80
0x7080
0x50607080
0x1020304050607080
&a
q = (short *) &a
r = (char *) &a
p = (int *) &a
Series:2. Pointers
14 Young Won Lim2/17/18
Pointer Type Cast
long a;
int *p;
short *q;
p
char *r;
0x10203040 0x50607080
p = (int *) &a
starting address
&a
*p 0x50607080
Series:2. Pointers
15 Young Won Lim2/17/18
Integer Pointer Types
long a;
int *p;
short *q; q
char *r;
0x10200x30400x50600x7080
q = (short *) &a
&a
*q 0x7080
Series:2. Pointers
16 Young Won Lim2/17/18
Integer Pointer Types
long a;
int *p;
short *q;
char *r; r
10 20 30 40 50 60 70 80
r = (char *) &a
&a
*r 0x80
Series:2. Pointers
17 Young Won Lim2/17/18
Re-interpretation of memory data – case II
10 20 30 40 50 60 70 80
&c
q = (short *) &c
a = (long *) &c
p = (int *) &cint *p;
short *q;
char *r;
long *a;
char c;
r = &c
Memory alignment constraint is not met
In this case, the memory alignment constraint can be broken
Series:2. Pointers
18 Young Won Lim2/17/18
Pointer Type Cast
char c;
&c
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
long *a;
Series:2. Pointers
19 Young Won Lim2/17/18
Pointer Type Cast
char c;
&c
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
int *p;
Series:2. Pointers
20 Young Won Lim2/17/18
Pointer Type Cast
char c;
&c
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
10 20 30 40 50 60 70 80
short *q;
Young Won Lim2/17/18
References
[1] Essential C, Nick Parlante[2] Efficient C Programming, Mark A. Weiss[3] C A Reference Manual, Samuel P. Harbison & Guy L. Steele Jr.[4] C Language Express, I. K. Chun[5] http://www.stackoverflow.com
