Steve Oualline
Practical C Programming
13. Simple Pointers183p
Pointers are also called
address variables because they contain the addresses of other variables.
184p
Pointers can be used as a quick and simple way to access arrays. (...) Pointers can be used to create new variables and complex data structures such as linked lists and trees.
185p
The operator ampersand (&) returns the address of a thing which is a pointer.
The operator asterisk (*) returns the object to which a pointer points.
Operator - Meaning
* - Dereference (given a pointer, get the thing referenced)
& - Address of (given a thing, point to it)
The operator ampersand (&) returns the address of a thing which is a pointer.
The operator asterisk (*) returns the object to which a pointer points.
int *thing_ptr; // declare a pointer to a thing
thing_ptr = &thing; // point to the thing
*thing_ptr = 5; // set "thing" to 5
// The expression &thing is a pointer to a thing. The variable thing is an object
// thing_ptr points to any integer. It may or may not point to the specific variable thing.
The & (address of operator) gets the address of an object (a pointer).
The * (dereference operator) tells C to look at the data pointed to, not hte pointer itself.
http://www.cplusplus.com/doc/tutorial/pointers.htmlhttp://www.cprogramming.com/tutorial/lesson6.html187p
Several pointers can point to the same thing.
188p
Pointers as Function ArgumentsThe only result of a function is a single return value.
http://en.wikipedia.org/wiki/Call_by_value#Call_by_valuehttp://www.cplusplus.com/doc/tutorial/functions2.htmlNULL pointer
locale.h
http://www.cplusplus.com/reference/clibrary/clocale/189p
const Pointersconst char *answer_ptr = "Forty-Two";
char *const name_ptr = "Test";
const char *const title_ptr = "Title";
191p
Pointers and Arrays(reminding...) 서 교수님:
number[10] 이라고 배열 선언을 하면 컴파일러는 10개의 연속된 데이터를 위한 공간을 확보하고 그 첫번째 공간의 주소를 number 에 넣습니다. 그래서 number 는 number[0] 의 주소를 가지는 것입니다.
number[1] 은 배열에서 number[0] 다음의 값을 가지는데 그 공간의 주소값을 알고 싶으면 &number[1] 이라고 하든지 number+1 이라고 하면 됩니다.
거꾸로, number 에서 시작하여 두번째 즉 number[1] 의 값을 주소로부터 얻고 싶으면 number[1] 이라고 하든지 *(number+1) 로 하여 얻을 수 있습니다.
192p
A pointer can be used to find each element of the array.
197p
Using Pointers to Split a Stringstrchr()
http://www.cplusplus.com/reference/clibrary/cstring/strchr.html201p
Pointers and StructuresInstead of having to move a lot of data around, we can declare an array of pointers and then sort the pointers.
Command-Line Argumentsmain (int argc, char *argv[])
{
The parameter argc is the number of arguments on the command line (including the program name).
The array argv contains the actual arguments.
(reminding...)
터미널에서, 말씀하신대로 "./V2008122-01 input.txt"라고 치면 다음과 같이 나옵니다.
argc=2
argv[0]=./V2008122-01
argv[1]=input.txt
서 교수님:
argv[0] = 실행프로그램 이름; 1번째는 항상 실행프로그램의 패스/이름 이 들어갑니다.
이번에는 argv[1] 에 들어갈 두 번째 값을 주었기 때문에 그 값이 프린트 된 것입니다.
command-line arguments는 shell 프로그램이 fileio 함수를 호출할 때 매개변수로 주는 것이고, 좀 더 엄밀하게는 OS 가 main 함수를 호출할 때 주는 것입니다.
http://www.cplusplus.com/reference/clibrary/cstdio/fprintf.htmlExample 13-12: print.c
// formats files for printing
// usage: print [options] file(s)
#include <stdio.h>
#include <stdlib.h>
int verbose = 0; // verbose mode (default = false)
char *out_file = "print.out"; //output filename
char *program_name; // name of the program for erros
int line_max = 66; // number of lines per page
void do_file(char *name)
{
printf("Verbose %d Lines %d Input %s Output %s\n",
verbose, line_max, name, out_file);
}
void usage (void)
{
fprintf(stderr, "Usage is %s [options] [file-list]\n",
program_name);
fprintf(stderr, "Options\n");
fprintf(stderr, " -v verbose\n");
fprintf(stderr, " -l<number> Number of line\n");
fprintf(stderr, " -o<name> Set output filename\n");
exit(8);
}
int main (int argc, char *argv[])
{
program_name =argv[0];
while ( (argc>1) && (argv[1][0] == '-') )
// argv[1][1] is the actual option character
{
switch (argv[1][1]) {
case 'v':
verbose = 1;
break;
case 'o':
out_file = &argv[1][2];
break;
case 'l':
line_max = atoi(&argv[1][2]);
break;
default:
fprintf(stderr, "Bad option %s\n", argv[1]);
usage();
}
++argv;
--argc;
}
if (argc == 1) {
do_file("printf.in");
}
else {
while (argc>1)
{
do_file(argv[1]);
++argv;
--argc;
}
}
return(0);
}
Xcode 실행창:
Verbose 0 Lines 66 Input printf.in Output print.out
terminal:
999:~/cintro/ch13/eg12 lym$ ./ch13eg12
Verbose 0 Lines 66 Input printf.in Output print.out
999:~/cintro/ch13/eg12 lym$ ./ch13eg12 i am tired
Verbose 0 Lines 66 Input i Output print.out
Verbose 0 Lines 66 Input am Output print.out
Verbose 0 Lines 66 Input tired Output print.out
999:~/cintro/ch13/eg12 lym$ ./ch13eg12 -v -l128 -0title xfile yfile zfile
Bad option -0title
Usage is ./ch13eg12 [options] [file-list]
Options
-v verbose
-l<number> Number of line
-o<name> Set output filename
999:~/cintro/ch13/eg12 lym$ ./ch13eg12 -v -l128 -otitle xfile yfile zfile
Verbose 1 Lines 128 Input xfile Output title
Verbose 1 Lines 128 Input yfile Output title
Verbose 1 Lines 128 Input zfile Output title
208p
A pointer does not create any new space for data, but just refers to data that is created elsewhere.
http://www.cplusplus.com/doc/tutorial/pointers.html
The identifier of an array is equivalent to the address of its first
element, as a pointer is equivalent to the address of the first element
that it points to, so in fact they are the same concept.
An array can be considered a constant pointer.
http://www.cprogramming.com/tutorial/lesson6.html
Arrays can act just like pointers.
