c/c++ memset用法

最新推荐文章于 2024-07-29 20:08:31 发布

原创最新推荐文章于 2024-07-29 20:08:31 发布 · 2.4k 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#class #iterator #output #function #algorithm #behavior

c++ 专栏收录该内容

13 篇文章

订阅专栏

本文详细介绍了C++内存填充函数memset的用法、参数解释、返回值及实例演示，并阐述了如何利用STL中的fill函数进行内存填充，提供了一段使用示例代码及其输出结果。

memset

Routine	Required header
memset	<memory.h> or <string.h>
wmemset	<wchar.h>

function

<cstring>

void * memset ( void * ptr, int value, size_t num );

Fill block of memory

Sets the first num bytes of the block of memory pointed by ptr to the specifiedvalue (interpreted as anunsigned char).

Parameters

ptr

Pointer to the block of memory to fill.

value

Value to be set. The value is passed as an int, but the function fills the block of memory using theunsigned char conversion of thisvalue.

num

Number of bytes to be set to the value.

Return Value

ptr is returned.

Example

1 2 3 4 5 6 7 8 9 10 11

/* 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;
}

Output:


------ every programmer should know memset!

注：需要注意的是memset是对第一个参数（指针）所指向的内存中（长度为第三个参数，单位是字节数），每个字节置为字符的ASCII码

也就是说不是以数据类型为单位进行置位的

int a[10];

memset(a,10,sizeof(a));

结果是把a所指向的内存区域每个字节置成了ASCII码10，那么结果自然不是想要的，也就是10 10 10 10（简写的），意思是4个字节中，每个内存都是10，4个自然不是咯！

但是可以给int（float……）或指针行数组初始化成0的；

int a[10];

memset(a,0,sizeof(a));

原理已经讲过了，就不再重复；

要想对int数组，或其他任意数组进行片操作，可以使用STL里的函数模板(fill)

需加头文件

#include <algorithm>

fill

function template

<algorithm>

template < class ForwardIterator, class T >
  void fill ( ForwardIterator first, ForwardIterator last, const T& value );

Fill range with value

Sets value to all elements in the range [first,last).

The behavior of this function template is equivalent to:

1 2 3 4 5

template < class ForwardIterator, class T >
  void fill ( ForwardIterator first, ForwardIterator last, const T& value )
{
  while (first != last)  *first++ = value;
}

Parameters

first, last

Forward iterators to the initial and final positions in a sequence. The range affected is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.

value

Value to be used to fill the range.

Return value

none

Example

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

// fill algorithm example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int main () {
  vector<int> myvector (8);                       // myvector: 0 0 0 0 0 0 0 0

  fill (myvector.begin(),myvector.begin()+4,5);   // myvector: 5 5 5 5 0 0 0 0
  fill (myvector.begin()+3,myvector.end()-2,8);   // myvector: 5 5 5 8 8 8 0 0

  cout << "myvector contains:";
  for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
    cout << " " << *it;

  cout << endl;
 
  return 0;
}