字符串之函数重写

---

0、readme

String summary

---

1、strlen

size_t strlen(const char* str)
{
     
    size_t i = 0;
  
    while (str[i] != '\0')  i++;
  
    return i;
}

---

2、strnlen

size_t strlen(const char* str, size_t maxlen)
{
     
    size_t i = 0;
  
    while (str[i] != '\0')  i++;
    
    if (i < maxlen)  return i;
    else  return maxlen;
      
    return i;
}

---

3、strcpy

char *strcpy(char* dest, const char* src)
{
     
    size_t i = 0;
  
    while (src[i] != 0) 
    {
     
        dest[i] = src[i];
        i++; 
    }

    dest[i] = 0;

    return dest;
}

---

4、strncpy

char *strncpy(char* dest, const char* src, size_t n)
{
     
    int len = (strlen(src) > n) ? n : strlen(src);

    size_t i = 0;
  
    for (i = 0; i < len; i++)
    {
      
        dest[i] = src[i]; 
    }

    dest[i] = 0;

    return dest;
}

---

5、strcmp

int strcmp(const char *str1, const char *str2 )
{
     
    int i = 0;
    int len = 0;  // str1和str2中较短字符串的长度。

    if (strlen(str1) > strlen(str2))  
        len = strlen(str2);
    else 
        len = strlen(str1);

    for (i = 0; i < len; ii++)
    {
     
      if (str1[i] == str2[i]) continue;
      else break;
    }

    // 两个字符串相同。
    if ((i == len) && (strlen(str1) == strlen(str2)) )
        return 0;

    // 两个字符串不同。
    if (str1[i] > str2[i]) return 1;

    return -1;
}

---

6、strncpy

int strncmp(const char *str1, const char *str2, const size_t n)
{
     
    int i = 0;

    for (i = 0; i < n; i++)
    {
     
        if (str1[i] == str2[i]) continue;
        else break;
    }

    // 两个字符串相同。
    if (i == n) return 0;

    // 两个字符串不同。
    if (str1[i] > str2[i]) return 1;

    return -1;
}

---

7、strcat

char *strcat(char* dest, const char* src)
{
     
    int destlen = strlen(dest);

    int i = 0;

    for (i = 0; i < strlen(src); i++)
    {
     
        dest[destlen + i] = src[i];
    }

    dest[destlen + i] = 0;

    return dest;
}

---

8、strncat

char *strncat(char* dest, const char* src, size_t n)
{
     
    int len = strlen(src);

    if (len > n)  len = n;
  
    int destlen = strlen(dest);

    int i = 0;

    for (i = 0; i < len; i++)
    {
     
        dest[destlen + i] = src[i];
    }

    dest[destlen + i] = 0;

    return dest;
}

---