strcpy,strncpy;strcat,strncat;memcpy,memncpy;

最新推荐文章于 2025-05-22 17:21:25 发布

原创最新推荐文章于 2025-05-22 17:21:25 发布 · 6.6k 阅读

7 ·

CC 4.0 BY-SA版权

C/C++ 专栏收录该内容

3 篇文章

订阅专栏

本文详细介绍了C语言中的字符串处理函数，包括strcpy用于完全复制字符串，strncpy限制复制字符数，strcat追加字符串，strncat限制追加字符数，以及内存复制函数memcpy和memmove的用法。通过源码分析，阐述了这些函数的工作原理和注意事项。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

strcat(str1,str2)：1）str1必须足够大；2）str1原来的'\0'被取消，只保留str2的'\0'，也就是str2从str1的'\0'位置开始占用；

哎，懒得写了，直接上源码了，我想说的再多，不如真真切切的看到其实现方式实在... ...呵呵.. ...

//linux2.6.10中源码

char * strcpy(char * dest,const char *src)
{
char *tmp = dest;

while ((*dest++ = *src++) != '\0')
/* nothing */;
return tmp;
}

可以看出，是将src中的'\0'一起拷贝了的.

char * strncpy(char * dest,const char *src,size_t count)
{
char *tmp = dest;

while (count) {
  if ((*tmp = *src) != 0) src++;
  tmp++;
  count--;
}
return dest;
}

size_t strlcpy(char *dest, const char *src, size_t size)
{
size_t ret = strlen(src);

if (size) {
  size_t len = (ret >= size) ? size-1 : ret;
  memcpy(dest, src, len);
  dest[len] = '\0';
}
return ret;
}

char * strcat(char * dest, const char * src)
{
char *tmp = dest;

while (*dest)
dest++;
while ((*dest++ = *src++) != '\0')
;

return tmp;
}

char * strncat(char *dest, const char *src, size_t count)
{
char *tmp = dest;

if (count) {
  while (*dest)
   dest++;
  while ((*dest++ = *src++) != 0) {
   if (--count == 0) {
    *dest = '\0';
    break;
   }
  }
}

return tmp;
}

size_t strlcat(char *dest, const char *src, size_t count)
{
size_t dsize = strlen(dest);
size_t len = strlen(src);
size_t res = dsize + len;

/* This would be a bug */
BUG_ON(dsize >= count);

dest += dsize;
count -= dsize;
if (len >= count)
len = count-1;
memcpy(dest, src, len);
dest[len] = 0;
return res;
}

int strcmp(const char * cs,const char * ct)
{
register signed char __res;

while (1) {
if ((__res = *cs - *ct++) != 0 || !*cs++)
break;
}

return __res;
}

int strncmp(const char * cs,const char * ct,size_t count)
{
register signed char __res = 0;

while (count) {
  if ((__res = *cs - *ct++) != 0 || !*cs++)
   break;
  count--;
}

return __res;
}

void * memcpy(void * dest,const void *src,size_t count)
{
char *tmp = (char *) dest, *s = (char *) src;

while (count--)
*tmp++ = *s++;

return dest;
}

void * memmove(void * dest,const void *src,size_t count)
{
char *tmp, *s;

if (dest <= src) {
  tmp = (char *) dest;
  s = (char *) src;
  while (count--)
   *tmp++ = *s++;
  }
else {
  tmp = (char *) dest + count;
  s = (char *) src + count;
  while (count--)
   *--tmp = *--s;
  }

return dest;
}