lecutre 05

这一讲中讲字符串的指针讲得很好Lecture05.pdflive_session.cmemory.cmemory_errors.cverify_password.cverify_password_soln.c
Side note: use strlen to get the length of a string. Don’t use sizeof!

Arrays of string

We create strings as char[], pass them around as char *


Q: Is there a way to check in code whether a string’s characters are modifiable?
A: No. This is something you can only tell by looking at the code itself and how the string was created.
Q: So then if I am writing a string function that modifies a string, how can I tell if the string passed in is modifiable?
A: You can’t! This is something you instead state as an assumption in your function documentation. If someone calls your function with a read-only string, it will crash, but that’s not your function’s fault :-)

一些程序例子

字符数组的负索引

#include <stdio.h>
#include <string.h>
void func(char *str) {
    str[0] = 'S';
    str++;
    *str = 'u';
    str = str + 3;
    str[-2] = 'm';
}
int main(int argc, const char *argv[]) {
    char buf[] = "Monday";
    printf("before func: %s\n", buf);
    func(buf);
    printf("after func: %s\n", buf);
    return 0;
}

输出，表明str[-2]是在当前str的位置向左查找了2个字符位置，从a到了m的位置。

char* vs char[] exercises

Bonus: Tricky addresses

void tricky_addresses() {
    char buf[] = "Local";
    char *ptr1 = buf;
    char **double_ptr = &ptr1;
    printf("double_ptr value: %p\n", double_ptr);
    printf("buf's address: %p\n", &buf);
    printf("ptr1's value: %s\n", ptr1);
    printf("ptr1’s deref: %c\n", *ptr1);
    printf("ptr1’s address: %p\n", &ptr1);
    printf("ptr1's value address: %p\n", ptr1);
    char *ptr2 = &buf;
    printf("ptr2's value: %s\n", ptr2);
    printf("ptr2’s deref: %c\n", *ptr2);
    printf("ptr2’s address: %p\n", &ptr2);
    printf("ptr2's value address: %p\n", ptr2);
}

lecture 06

这一讲很好Lecture06.pdflive_session.cskip_spaces.cskip_spaces_soln.c

Pointers & C Parameters

Pointers Summary

• If you are performing an operation with some input and do not care about any changes to the input, pass the data type itself.
• If you are modifying a specific instance of some value, pass the location of what you would like to modify.
• If a function takes an address (pointer) as a parameter, it can go to that address if it needs the actual value.

Double Pointers

Arrays in Memory

Arrays of Pointers

Pointer Arithmetic

const

struct

ternary

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