019

模拟实现strcpy()

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>

char *my_strcpy(char *dest, const char *src)
{
    char *ret = dest;
    assert(dest != NULL);
    assert(src != NULL);
    while (*dest++ = *src++)
    {
        ;
    }
    return ret;
}

int main()
{
    char *str1 = "abcdef";
    char str2[20] = { 0 };
    printf("%s\n", my_strcpy(str2, str1));
    system("pause");
    return 0;
}

模拟实现strcat()

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>

char *my_strcat(char *dest, const char *src)
{
    char *ret = dest;
    assert(dest != NULL);
    assert(src != NULL);
    while (*dest!='\0')
    {
        dest++;
    }
    while (*dest++ = *src++)
    {
        ;
    }
    return ret;
}

int main()
{
    char str1[20] = "abcd";
    const char *str2 = "efg";
    printf("%s\n", my_strcat(str1, str2));
    system("pause");
    return 0;
}

模拟实现strstr()

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>

char * my_strstr(char *str, char *substr)
{
    assert(str != NULL);
    assert(substr != NULL);
    char *s1 = str;
    char *s2 = substr;
    char *cur = str;
    while (*cur)
    {
        s1 = cur;
        s2 = substr;
        while (*s1 == *s2)
        {
            s1++;
            s2++;
        }
        if (*s2 == '\0')
            return cur;
        if (*s1 == '\0')
            return NULL;
        cur++;
    }
    return NULL;
}

int main()
{
    char arr1[] = "abcabcdabcg";
    char arr2[] = "abcd";
    printf("%s\n", my_strstr(arr1, arr2));
    system("pause");
    return 0;
}

模拟实现strchr(）

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>

char *my_strchr(const char *s, char c)
{
    char *ret = NULL;
    assert(s != NULL);
    while (*s)
    {
        if (*s == c)
        {
            ret = (char *)s;
            return ret;
        }
        s++;
    }
    return NULL;
}
int main()
{
    char arr[] = "abcdef";
    char a = 'g';
    printf("%s\n", my_strchr(arr, a));
    system("pause");
    return 0;
}

模拟实现strcmp()

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>

int my_strcmp(const char *str1, const char *str2)
{
  assert(str&&str2);
    while (*str1 == *str2)
    {
        if (*str1 == '\0')
        return 0;
        str1++;
        str2++;
    }

    if ((*str1 - *str2) > 0)
        return 1;
    else
        return -1;
}

int main()
{
    char *str1 = "abaz";
    char *str2 = "abaz";
    int ret = my_strcmp(str1, str2);
    if (ret == 0)
        printf("str1==str2\n");
    else  if (ret > 0)
        printf("str1>str2\n");
    else
        printf("str1<str2\n");
    system("pause");
    return 0;
}

模拟实现memcpy()

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>

void * my_memcpy(void *str1, const void *str2, size_t num)
{
    void *ret = str1;
    unsigned int i = 0;
    assert(str1&&str2);
    for (i = 0; i < num; i++)
    {
        *(char *)str1 = *(char *)str2;
        ++(char *)str1;
        ++(char *)str2;
    }
    return ret;
}

int main()
{
    int arr1[20] = { 1, 2, 3, 45 };
    int arr2[20] = { 1, 5, 5, 5, 5, 5, 5 };
    my_memcpy(arr1 + 2, arr2, 3 * sizeof(arr2[0]));
    system("pause");
    return 0;
}

模拟实现memmove(）

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>

void * my_memmove(void *str1, const void *str2, size_t num)
{
    void *ret = str1;
    assert(str1&&str2);
    if (str1 < str2)
    {
        while (num--)
        {
            *(char *)str1 = *(char *)str2;
            str1 = (char *)str1 + 1;
            str2 = (char *)str2 + 1;
        }
    }
    else
    {
        while (num--)
        {
            *((char *)str1 + num) = *((char *)str2 + num);
        }
    }
    return ret;
}

int main()
{
    int arr[20] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
    my_memmove(arr + 3, arr + 5, 8 * sizeof(arr[0]));
    system("pause");
    return 0;
}