《C和指针》——字符串操作补、字符串内存操作

1.对于 *string++!='\0',它其实等价于：

*string!='\0';
string++;

2.对于 strcpy函数，如果要复制的字符串比老字符串短，由于新字符串是以NUL（即’\0’）结尾，所以老字符串最后剩余的几个字符也会被有效地删除。
如：

char message[ ]=="Original message";
strcpy(message,"Different");

此时message=”Different”

3.同样使用strcpy和strcat时，目标字符数组的空间要足以容纳需要复制的字符串。

字符串内存操作

这些函数都在#include <cstring>

1.void *memcpy(void *dst,void const *src,size_t length);
其实就是从src的起始位置复制length个元素到dst的内存起始位置
例子：

#include <stdio.h>
#include <string.h>struct {char name[40];int age;
} person, person_copy;int main()
{char myname[] = "Pierre de Fermat";/* using memcpy to copy string: */memcpy(person.name, myname, strlen(myname) + 1);person.age = 46;/* using memcpy to copy structure: */memcpy(&person_copy, &person, sizeof(person));printf("person_copy: %s, %d \n", person_copy.name, person_copy.age);return 0;
}

输出：
person_copy: Pierre de Fermat, 46

2.void *memmove(void *dst,void const *src,size_t length);
移动src开始的length个元素移动到dst开始的位置
例子：

/* memmove example */
#include <stdio.h>
#include <string.h>int main ()
{char str[] = "memmove can be very useful......";memmove (str+20,str+15,11);puts (str);return 0;
}

输出：
memmove can be very very useful.

3.int *memcmp(void const *a,void const *b,size_t length);
a>b，返回值大于0
a=b，返回值等于0
a

/* memcmp example */
#include <stdio.h>
#include <string.h>int main ()
{char buffer1[] = "DWgaOtP12df0";char buffer2[] = "DWGAOTP12DF0";int n;n=memcmp ( buffer1, buffer2, sizeof(buffer1) );if (n>0) printf ("'%s' is greater than '%s'.\n",buffer1,buffer2);else if (n<0) printf ("'%s' is less than '%s'.\n",buffer1,buffer2);else printf ("'%s' is the same as '%s'.\n",buffer1,buffer2);return 0;
}

输出：
‘DWgaOtP12df0’ is greater than ‘DWGAOTP12DF0’.

4.void *memchr(void const *a,int ch,size_t length);
从a开始的length元素个数中找ch出现的第一个位置
例子：
/* memchr example */

#include <stdio.h>
#include <string.h>int main()
{char * pch;char str[] = "Example string";pch = (char*)memchr(str, 'p', strlen(str));if (pch != NULL)printf("'p' found at position %d.\n", pch - str + 1);elseprintf("'p' not found.\n");return 0;
}

输出：
‘p’ found at position 5.

5.void * memset ( void * a, int ch, size_t length );
从a的开始的length元素都设置为值ch。
例子：

/* memset example */
#include <stdio.h>
#include <string.h>int main()
{char str[] = "almost every programmer should know memset!";memset(str, '-', 6);puts(str);return 0;
}

输出：

—— every programmer should know memset!