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[英]initialize struct array element with different value using memset in c++
[英]Using memset and memcpy correctly to initialize a character array in C++
我想使用來自字符指針的數據來初始化字符數組。 我為此編寫了以下代碼:
(請原諒我對結構和所有結構所做的事情。實際上,此代碼應該適合更大的結構,因此該結構及其用途很奇怪)
#include <iostream>
#include <string>
struct ABC
{
char a;
char b;
char c[16];
};
int main(int argc, char const *argv[])
{
struct ABC** abc;
std::string _r = "Ritwik";
const char* r = _r.c_str();
if (_r.length() <= sizeof((*abc)->c))
{
int padding = sizeof((*abc)->c) - _r.length();
std::cout<<"Size of `c` variable is : "<<sizeof((*abc)->c)<<std::endl;
std::cout<<"Value of padding is calculated to be : "<<padding<<std::endl;
char segment_listing[ sizeof((*abc)->c)];
std::cout<<"sizeof segment_listing is "<<sizeof(segment_listing)<<std::endl;
memcpy(segment_listing, r, _r.length());
memset( (segment_listing + _r.length()), ' ', padding);
std::cout<<segment_listing<<std::endl;
}
return 0;
}
但是,當我運行代碼時,我在字符串的末尾得到了這些奇怪的字符:
(rh4dev01:~/rough) rghosh> ./crptr
Size of `c` variable is : 16
Value of padding is calculated to be : 10
sizeof segment_listing is 16
Ritwik °×
(rh4dev01:~/rough) rghosh> ./crptr
Size of `c` variable is : 16
Value of padding is calculated to be : 10
sizeof segment_listing is 16
Ritwik Ñ
(rh4dev01:~/rough) rghosh> ./crptr
Size of `c` variable is : 16
Value of padding is calculated to be : 10
sizeof segment_listing is 16
Ritwik g
(rh4dev01:~/rough) rghosh> ./crptr
Size of `c` variable is : 16
Value of padding is calculated to be : 10
sizeof segment_listing is 16
Ritwik pô
(rh4dev01:~/rough) rghosh> ./crptr
Size of `c` variable is : 16
Value of padding is calculated to be : 10
sizeof segment_listing is 16
Ritwik
(rh4dev01:~/rough) rghosh> ./crptr
Size of `c` variable is : 16
Value of padding is calculated to be : 10
sizeof segment_listing is 16
Ritwik àå
(rh4dev01:~/rough) rghosh> ./crptr
Size of `c` variable is : 16
Value of padding is calculated to be : 10
sizeof segment_listing is 16
Ritwik »
(rh4dev01:~/rough) rghosh> ./crptr
Size of `c` variable is : 16
Value of padding is calculated to be : 10
sizeof segment_listing is 16
Ritwik pZ
你能解釋為什么會這樣嗎? 因為我只打印一個字符數組,所以長度僅為16個字符,難道不應該只打印16個字符嗎? 那兩個(有時是零,有時是一個)字符從哪里來?
更重要的是,我是否通過填充破壞了任何內存(不屬於我的字符數組c
)?
您的字符串需要NUL終止。
memcpy(segment_listing, r, _r.length());
memset( (segment_listing + _r.length()), ' ', padding-1);
segment_listing[_r.length() + padding - 1] = '\0';
使用snprintf()
可能會更好地為您服務,它將為您添加終止符:
snprintf(segment_listing, sizeof(segment_listing), "%-*s",
(int)sizeof(segment_listing)-1, r);
AC字符串以0字節結尾,您在任何地方都沒有考慮。 您需要以0終止字符串,並且在所有計算中都必須考慮到該額外字節。
segment_listing
沒有空字符
const int SIZE = 16; //or 17 if you want 16 + null char
//pre-initialise array - then will automatically be null terminated
char segment_listing[SIZE] = {0};
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