C语言学习记录——模拟字符串相关函数（strcpy、strlen、strcat）相关知识-const、typedef

#include <stdio.h>
#include <string.h>
int main()
{
    char arr1[20] = { "xxxxxxxxxxxxxx" };
    char arr2[10] = { "hello" };
    //arr1为目标空间的起始地址，arr2为要源空间的起始地址
    strcpy(arr1, arr2);
    //运行之后将arr2复制到arr1中（包括‘\0’）
    printf("%s\n", arr1);
    return 0;
}

#include <stdio.h>
#include <assert.h>
char* my_strcpy(char* strDestination, const char* strSource)//const防止源空间初始地址被修改
{   
    assert(strSource != NULL);//断言
    assert(strDestination != NULL);//断言
    //此处断言是为了目标空间初始地址或源空间初始地址为空指针时能够准确报错
    char* ret = strDestination;//还原库函数，有返回值
    while (*strDestination++ = *strSource++)
        ;//hello的拷贝
    return ret;
}
 
int main()
{
    char arr1[20] = { "xxxxxxxxxxxxxx" };
    char arr2[10] = { "hello" };
    printf("%s\n", my_strcpy(arr1,arr2));
    return 0;
}

int main()
{
    const int i;
    const int* p;
    int *const b;
    int const* const pb;
    i = 10;//error
    *p = 10;//error
    b = &i;//error
    *pb = 20;//error
    pb = &i;//error
    return 0;
}

#include <stdio.h>
#include <string.h>
int main()
{
    char arr[] = { "indispensable" };
    printf("leng = %d\n", strlen(arr));
    return 0;
}

#include <stdio.h>
#include <assert.h>
//size_t -- unsigned int
size_t my_strlen(const char* strDestination)
{
    assert(strDestination != NULL);//assert(strDestination);
    size_t count = 0;
    while (*strDestination++ != '\0')
        count++;
    return count;
}
 
int main()
{
    char arr[] = { "indispensable" };
    printf("leng = %d\n", my_strlen(arr));
    return 0;
}

typedef unsigned int     size_t;

//第一个
typedef unsigned long ulong;
 
ulong ul;     // 相当于 "unsigned long ul;"
 
//第二个
typedef struct mystructtag
{
   int   i;
   float f;
   char  c;
} mystruct;
 
mystruct ms;   //相当于 "struct mystructtag ms;"
 
//第三个
typedef int (*funcptr)();  // funcptr 表示指向函数整型返回值
 
funcptr table[10];   // 相当于 "int (*table[10])();"

#include <stdio.h>
#include <string.h>
int main()
{
    char arr1[100] = { "love " };
    char arr2[100] = { "and " };
    char arr3[100] = { "peace " };
    strcat(arr1, arr2);
    strcat(arr1, arr3);
    printf("%s\n", arr1);
    return 0;
}

#include <stdio.h>
#include <assert.h>
char* my_strcat(char* strDestination, const char* strSource)
{
    assert(strSource != NULL);//断言
    assert(strDestination != NULL);//断言
    char* ret = strDestination;
    while (*strDestination)
        *strDestination++;
    while (*strDestination++ = *strSource++)
        ;
    return ret;
}
int main()
{
    char arr1[100] = { "love " };
    char arr2[100] = { "and " };
    char arr3[100] = { "peace " };
    my_strcat(arr1, arr2);
    my_strcat(arr1, arr3);
    printf("%s\n", arr1);
    return 0;
}