c语言进阶部分详解（详细解析字符串常用函数，并进行模拟实现（上））

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<string.h>
int main()
{
  char arr[] = "hello";
  printf("%s的长度是%d", arr, strlen(arr));
  return 0;
}

size_t my_strlen(char* pa)
{
  assert(pa);
  int count = 0;
  while (*pa)
  {
    count++;
    pa++;
  }
  return count;
}
int main()
{
  char arr[] = "hello";
  printf("%s的长度是%d", arr, my_strlen(arr));
  return 0;
}1. size_t my_strsize_t my_strlen(char* pa)
{
  assert(pa);
  int count = 0;
  while (*pa)
  {
    count++;
    pa++;
  }
  return count;
}
int main()
{
  char arr[] = "hello";
  printf("%s的长度是%d", arr, my_strlen(arr));
  return 0;
}

size_t my_strlen(char* pa)
{
  if (*pa)
  {
    return my_strlen(pa + 1) + 1;
  }
  else
  {
    return 0;
  }
}
int main()
{
  char arr[] = "hello";
  printf("%s的长度是%d", arr, my_strlen(arr));
  return 0;
}

size_t my_strlen(char* pa)
{
  char* start = pa;
  while (*pa)
  {
    pa++;
  }
  return pa - start;
}
int main()
{
  char arr[] = "hello";
  printf("%s的长度是%d", arr, my_strlen(arr));
  return 0;
}

int main() 
{
    char src[] = "Hello, world!";
    char dest[20];
    strcpy(dest, src);
    printf("The copied string is: %s\n", dest);
    return 0;
}

char* my_strcpy(char* dest, char* src)
{
    while (*src)
    {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = *src;
}
int main() 
{
    char src[] = "Hello, world!";
    char dest[20];
    my_strcpy(dest, src);
    printf("The copied string is: %s\n", dest);
    return 0;
}

char* my_strcpy(char* dest, char* src)
{
    char* ret = dest;
    while (*dest++ = *src++)
    {
        ;
    }
    return ret;
}
int main() 
{
    char src[] = "Hello, world!";
    char dest[20];
    my_strcpy(dest, src);
    printf("The copied string is: %s\n", dest);
    return 0;
}

int main()
{
  char arr1[20] = "hello";
  char arr2[] = " world";
  printf("%s", strcat(arr1, arr2));
  return 0;
}

char* my_strcat(char* dest, char* src)
{
  char* ret = dest;
  while (*dest)
  {
    dest++;
  }
  while (*src)
  {
    *dest = *src;
    dest++;
    src++;
  }
  *dest = *src;
  return ret;
}
int main()
{
  char arr1[20] = "hello";
  char arr2[] = " world";
  printf("%s", my_strcat(arr1, arr2));
  return 0;
}

int main()
{
  char arr1[] = "abc";
  char arr2[] = "aec";
    int result = strcmp(arr1, arr2);
    if (result < 0) {
        printf("arr1 is less than arr2\n");
    }
    else if (result > 0) {
        printf("arr1 is bigger than arr2\n");
    }
    else {
        printf("arr1 is equal to arr2\n");
    }
  return 0;
}

int my_strcmp(char* arr1, char* arr2)
{
    while (*arr1 == *arr2)
    {
        if (*arr1 == '\0' && *arr2 == '\0')
        {
            return 0;
        }
        arr1++;
        arr2++;
    }
    return *arr1 - *arr2;
}
int main()
{
  char arr1[] = "abc";
  char arr2[] = "aec";
    int result = my_strcmp(arr1, arr2);
    if (result < 0) {
        printf("arr1 is less than arr2\n");
    }
    else if (result > 0) {
        printf("arr1 is bigger than arr2\n");
    }
    else {
        printf("arr1 is equal to arr2\n");
    }
  return 0;
}

#include <string.h>
char *strncpy(char *dest, const char *src, size_t n);

int main() 
{
    char src[] = "Hello, World!";
    char dest[20];
    strncpy(dest, src, 5);
    dest[5] = '\0';
    printf("Copied string: %s\n", dest);
    return 0;
}

#include<stdio.h>
#include<string.h>
int main() 
{
    char dest[20] = "Hello, ";
    char src[] = "World!";
    strncat(dest, src, 5);
    printf("Connected string: %s\n", dest);
    return 0;
}

int main() {
    char str1[] = "Hello";
    char str2[] = "Hell";
    int result = strncmp(str1, str2, 4);
    if (result == 0) 
    {
        printf("The first 4 characters of str1 and str2 are equal.\n");
    }
    else if (result < 0) 
    {
        printf("The first different character in str1 is smaller than the corresponding character in str2.\n");
    }
    else 
    {
        printf("The first different character in str1 is bigger than the corresponding character in str2.\n");
    }
    return 0;
}