Buffer Manipulation Functions

Buffer Manipulation functions allow you to manipulate or compare characters stored in data buffers. These functions begin with the mem prefix. Expand the category to view a list of the available functions.

memchr

void *memchr(const void *s,int c,size_t n);

s: The name of the buffer.

c: The character to search for in the buffer.

n:The number of characters at the beginning of the buffer to search.

//以下的例子是在字符串"Example string"中搜索字符'x'出现的第一个位置

   char * p;

   char str[] = "Example xtring";

        //获取第一个字符在内存中的位置

        lr_output_message("The first character is at buffer %d",str);

        //搜索整个字符串，获取'x'在内存中的位置

   p = (char *)memchr(str, 'x', strlen(str));

   if (p) {

 //打印出获取'x'在内存中的位置

 lr_output_message ("Character x is at buffer %d\n", p);

 //打印出获取'x'在字符串中的位置，'x'的位置是内存中相对位置+1

 lr_output_message ("Character x is at position %d\n", p - str + 1);

 }

   else

       lr_output_message ("Character x was not found");

memcmp

int memcmp(const viod *s1,const void *s2,size_t n);

s1: The name of a buffer.

Se: The name of a buffer.

n:The number of characters to search at the beginning of the buffer.

//以下的例子是用memcmp来比较两个字符串是否相等。

char *s1="access to shared transmission";

char *s2="access to transmission";

int rc;

//通过memcmp返回值与0比较大写来确认字符串大小

rc =memcmp(s1,s2,strlen(s1));

if(rc>0)

lr_output_message("'%s' is greater than '%s'",s1,s2);//s1>s2

else if (rc<0)

lr_output_message("'%s' is less than '%s'",s1,s2);//s1<s2

else

lr_output_message("'%s' is equal to '%s'",s1,s2);//s1=s2

memcpy

Void *memcpy(void *dest,const void *src,size_t n);

dest: Destination buffer where the data is copied

src: The name of the source buffer from which from the data is copied.

n: The number of bytes to copy

char s1[] = "Sample string",s3[]="Just testing";

char s2[40],s4[40];

/* +1是为了复制s1的结束符号(NULLterminator) */

memcpy(s2, s1, strlen(s1)+1);

lr_output_message("s1=%s s2=%s", s1, s2);

/* -1使得s4比比s3少一位*/

memcpy(s4, s3, strlen(s3)-1);

lr_output_message("s3=%s s4=%s", s3, s4);

memmove

void *memmove(void *dest,const void *src,size_t n);

dest:Destination buffer where the data is copied.

src:The name of the source buffer from which the data is copied.

n:The number of bytes to copy.

char buffer[80];

strcpy(buffer,"abcde");

//把'abcde'的前四位'abcd'拼接到自身字符串从第二位开始的位置''

memmove(buffer+1,buffer,4);

lr_output_message("New string: %s\n",buffer);

memset

void *memset(void *buffer,int c,size_t n);

buffer:Pointer to block of data to be filled with c.

c:The character placed in buffer.

n:The number of bytes in buffer set as c.

//在初始化之前memset填充结构about_app中所有元素为0

        //定义结构about_app

        struct about_app {

                  char *version;

                  int field1;

                  int field2;

       }a;

        //赋值

        a.field1=12;

        a.field2=13;

        //使用0填充所有的fields

        memset(&a,0,sizeof(struct about_app));

        //打印出所有的fields查看是否为0。

        lr_output_message("After memset field1=%d field2=%d",a.field1,a.field2);

        //初始化结构，并赋初值。

        a.version="app version1.0";

        a.field1=5;

        a.field2=6;

        lr_output_message("Now,field1=%d field2=%d",a.field1,a.field2);