嵌入式Linux C（六）——字符串

char *ptr = "hello world";//保存在数据段的or段，改数据不能被修改（常量字符串，不能被修改）
char src[100] = "hello world";//保存在栈
char *str = (char *) malloc(sizeof(char) * 100);//保存在堆
strcpy(str,"hello world");

char src[100] = "hello world";
char *str = (char *) malloc(sizeof(char) * 100);
if(NULL == str)
{
  printf("malloc error!");
  exit(1);
}
size_t len = strlen(src);//返回是长整型
printf("%ld",len);
//实现
size_t my_strlen(const char *s)
{
  size_t len = 0;
  whlie(*s != '\0')
  {
  len++;
  s++;
  }
  return len;
}

char src[100] = "hello world";
char *dest = (char *) malloc(sizeof(char) * 100);
if(NULL == dest)
{
  printf("malloc error!\n");
  exit(1);
}
char *temp = strcpy(dest,src);//返回dest的首字符地址
//存在风险，无法确定dest是否大于src。
//微软推荐strcpy_s(char *dest,int len,char *src)len就是dest的长度
if(NULL == temp)//相对于my_strcpy而言
{
  printf("my strcpy is error!\n");
  exit(1);
}
//实现my_strcpy
char *my_strcpy(char *dest,char *src)
{
  if(NULL  == dest || NULL == src)
  {
  return NULL;
  }
  char *temp = dest;//需要有个temp进行移动
  whlie(*src != '\0')
  {
  *temp = *src;
  src++;
  temp++;
  }
  *dest = '\0';
  return dest;
}
//my_str_strncpy
char *my_strncpy(char *dest,char *src,size_t n)
{
  if(NULL  == dest || NULL == src)
  {
  return NULL;
  }
  int i;
  char *temp = dest;
  for(i = 0; (i < n) && (*src != '\0'); i++)
  {
  *temp = *src
  src++;
  temp++;
  }
  for(;i < n;i++)
  {
  *temp = '\0';
  temp++;
  }
  return dest;
}

//实现my_strcat
char *my_strcat(char *dest,char *src)
{
  if(NULL  == dest || NULL == src)
  {
  return NULL;
  }
  char *temp = dest;
  while(*temp != '\0')
  {
  temp++;
  }
  while(*src != '\0')
  {
  *temp = *src;
  temp++;
  src++;
  }
  *temp = '\0';
  return dest;
}
//实现my_strcat
char *my_strncat(char *dest,char *src,size_t n)
{
  if(NULL  == dest || NULL == src)
  {
  return NULL;
  }
  char *temp = dest;
  while(*temp != '\0')
  {
  temp++;
  }
  for(int i = 0; (i < n) && (*src != '\0'); i++)
  {
  *temp = *src;
  temp++;
  src++;
  }
  *temp = '\0';
  return dest;
}

//实现
int my_strcmp(char *s1,char *s2)
{
  if(NULL == s1 && NULL != s2)
  {
  return -1;
  }
  if(NULL != s1 && NULL == s2)
  {
  return 1;
  }
  if(NULL == s1 && NULL == s2)
  {
  return 0;
  }
  while(*s1 != '\0' &&)
  {
  if(*s1 > *s2)
  {
    return 1;
  }
  if(*s1 < *s2)
  {
    return 0;
  }
  s1++;
  s2++;
  }
  if(*s1 == '\0' && *s2 == '\0')
  {
  return 0;
  }
  if(*s1 != '\0' && *s2 == '\0')
  {
  return 1;
  }
  if(*s1 == '\0' && *s2 != '\0')
  {
  return -1;
  }
  return 0;
}

//实现strncmp
int my_strncmp(char *s1,char *s2,size_n)
{
  if(NULL == s1 || s2 == NULL)
  {
  return -1;
  }
  for(int i = 0; (i < n) && ((s1[i] != '\0') && (s2 != '\0')); i++)
  {
  if(s1[i] != s2[i])
  {
    return -1;
  }
  }
  return 0;
}