04.Memory-筆記

測驗
https://sandbox.cs50.io/
https://cs50.harvard.edu/x/2020/weeks/2/
https://www.youtube.com/watch?v=cF6YkH-8vFk
20mins
十六進制
Hex Decimal
RGB
FFFFFF
255,255,255

#include <stdio.h>

int main(void)
{
    int n = 50;
    printf("%i\n", n); 
    // 50
}

---

“＆”號表示地址是什麼，
“*”表示前往某個地址。

// Prints an integer's address

#include <stdio.h>

int main(void)
{
    int n = 50;
    printf("%p\n", &n);
}
// 0x7ffe00b3adbc 

// Prints an integer via its address

#include <stdio.h>

int main(void)
{
    int n = 50;
    printf("%i\n", *&n);
    // 50
}

// Stores and prints an integer's address

#include <stdio.h>

int main(void)
{
    int n = 50;
    int *p = &n;
    printf("%p\n", p);
    // // 0x7ffe00b3adbc 
}

// Stores and prints an integer's address

#include <stdio.h>

int main(void)
{
    int n = 50;
    int *p = &n;
    printf("%i\n", p);
    // <!-- ：您將n的地址存儲在p和p中
    //18:41
    //是一個指針，特別是指向整數的指針。
    //18:45
    //換句話說，p是整數的地址。 -->
}

06 / 30

Char start means s is storing the address of a character

? What must getString returing
The index of the first letter.
string s = EMMA;
s pointer = > EMMA

E 0x123
M 0x124
M 0x125
A 0x126
\0 0x127

#include <stdio.h>

int main(void)
{
    char *s = "EMMA";
    printf("%p\n", s);
    printf("%p\n", &s[0]);
    printf("%p\n", &s[1]);
    printf("%p\n", &s[2]);
    printf("%p\n", &s[3]);
    // ---------------------
    printf("%c\n", *s);
    printf("%c\n", *(s+1));
    printf("%c\n", *(s+2));
    printf("%c\n", *(s+3));
    printf("%c\n", *(s+4));
}


0x42ab52
0x42ab52
0x42ab53
0x42ab54
0x42ab55

E
M
M
A

{
    int n = 50;
    int *p = &n;

    printf("%p\n", &n);
    printf("%i\n", *&n);
    printf("---------------\n");

    int t = 50;
    int *a = &t;
    printf("%i\n", t);
    printf("%p\n", &t);
    printf("---------------\n");
    string s = "EMMA";
    printf("%s\n", s);
    printf("%p\n", s);
}
$ ./address 
0x7ffcb3111d9c
50
---------------
50
0x7ffcb3111d8c
---------------
EMMA
0x42aac7

---

compare

#include <cs50.h>
#include <stdio.h>

int main(void)
{
    int i = get_int("i: ");
    int j = get_int("j: ");

    if(i == j)
    {
        printf("Same\n");
    }
    else 
    {
        printf("Defferent\n");
    }
}


$ ./compare 
i: 1
j: 2
Different

COMPARE

#include <cs50.h>
#include <stdio.h>

int main(void)
{
    // int i = get_int("i: ");
    // int j = get_int("j: ");

    // string s = get_string("s: ");
    // string t = get_string("t: ");

    char *s  = get_string("s: ");
    char *t  = get_string("t: ");
    // Char start means s is storing the address of a character  
    printf("%p\n", s);
    printf("%p\n", t);
    if(s == t)
    {
        printf("Same\n");
    }
    else 
    {
        printf("Defferent\n");
    }
}

$ ./compare
s: EM
t: EM
0x1ffe6a0
0x1ffe6e0
Defferent
我輸入 都是EM 為何會是DIFFERENT
原因在記憶體位置

---

COPY

// Capitalizes a string

#include <cs50.h>
#include <ctype.h>
#include <stdio.h>
#include <string.h>

int main(void)
{
    // Get a string
    string s = get_string("s: ");

    // Copy string's address
    string t = s;

    // Capitalize first letter in string
    if (strlen(t) > 0)
    {
        t[0] = toupper(t[0]);
    }

    // Print string twice
    printf("s: %s\n", s);
    printf("t: %s\n", t);
}
$ ./copy 
s: EMMA
s: EMMA
t: EMMA

我只要 將s 轉大寫 並不想要連t 一起

下面一個例子
malloc 50:00
for memory alloca

// Capitalizes a copy of a string

#include <cs50.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void)
{
    // Get a string
    char *s = get_string("s: ");

    // Allocate memory for another string
    char *t = malloc(strlen(s) + 1);

    // Copy string into memory
    for (int i = 0, n = strlen(s); i <= n; i++)
    {
        t[i] = s[i];
    }

    // Capitalize copy
    t[0] = toupper(t[0]);

    // Print strings
    printf("s: %s\n", s);
    printf("t: %s\n", t);
}

strcpy , strlen

when you pass inputs to a function , you are effectively passing copies of your own values to that function

the heap is a big chunk of meomory where you can alloate memory form.

Clang

machine code ↓	1
globals ↓	2
heap ↓	3
.	4
.	5
stack ↑	6

swap 1:22:00

.	6
.	5
.	4
.	3
1a 2b swap	2
main ↑ 1x 2y	1

scanf

// Dangerously gets a string from user using scanf

#include <stdio.h>

int main(void)
{
    char s[5];
    printf("s: ");
    scanf("%s", s);
    printf("s: %s\n", s);
}