📜  C++中的记忆集

📅  最后修改于: 2021-05-30 13:59:03             🧑  作者: Mango

将值ch转换为无符号char,并将其复制到str []指向的对象的前n个字符中的每个字符中。如果对象不是普通可复制的(例如,标量,数组或C兼容结构),则行为是不确定的。如果n大于str指向的对象的大小,则该行为是不确定的。
模板

void* memset( void* str, int ch, size_t n);
Parameters
str[] : Pointer to the object to copy the character.
ch : The character to copy.
n : Number of bytes to copy.
Return value :
The memset() function returns str, the pointer to the destination string. 
CPP
// CPP program to illustrate memset
#include 
#include 
 
using namespace std;
 
int main()
{
    char str[] = "geeksforgeeks";
    memset(str, 't', sizeof(str));
    cout << str;
    return 0;
}


CPP
#include 
using namespace std;
  
int main()
{
    int a[5];
  
    // all elements of A are zero
    memset(a, 0, sizeof(a));
    for (int i = 0; i < 5; i++)
        cout << a[i] << " ";
    cout << endl;
  
    // all elements of A are -1
    memset(a, -1, sizeof(a));
    for (int i = 0; i < 5; i++)
        cout << a[i] << " ";
    cout << endl;
  
    // Would not work
    memset(a, 5, sizeof(a)); // WRONG
    for (int i = 0; i < 5; i++)
        cout << a[i] << " ";
}


输出:

tttttttttttttt

对于整数数据类型,我们可以使用memset()将所有值设置为0或-1。如果将其设置为其他值,它将不起作用。原因很简单,memset逐字节工作。

CPP

#include 
using namespace std;
  
int main()
{
    int a[5];
  
    // all elements of A are zero
    memset(a, 0, sizeof(a));
    for (int i = 0; i < 5; i++)
        cout << a[i] << " ";
    cout << endl;
  
    // all elements of A are -1
    memset(a, -1, sizeof(a));
    for (int i = 0; i < 5; i++)
        cout << a[i] << " ";
    cout << endl;
  
    // Would not work
    memset(a, 5, sizeof(a)); // WRONG
    for (int i = 0; i < 5; i++)
        cout << a[i] << " ";
}

输出:

0 0 0 0 0 
-1 -1 -1 -1 -1 
84215045 84215045 84215045 84215045 84215045
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