C ++将指针传递给向量元素而不是数组指针

问题描述

我认为下面的代码片段是完全合法的（它建立在MS Visual Studio 2008，C + +）。

I think the following code snippet is perfectly legal (it builds anyway on MS Visual Studio 2008, C++).

我使用它链接到第三方库。但我认为，因为我传递一个向量元素的指针，而不是第三方库函数期望的常规指针，我得到运行时错误

I use it to link to a 3rd party library. But I think because I am passing a pointer to a vector element instead of a regular pointer that the 3rd party library function expects, I get a run-time error

我在这里做什么？

std::vector<int> vec_ints(27,0);
std::vector<double> vec_doub(27, 0.);
for(int i = 0; i < n; ++i) {
   //-Based on my understanding when i >=27, STL vectors automatically reallocate additional space (twice).
   vec_ints[i] = ...;
   vec_doub[i] = ...;
}
const int* int_ptr = &vec_ints[0];
const double* doub_ptr = &vec_doub[0];
//-Func is the 3rd party library function that expects a const int* and const double* in the last 2 arguments.
func(...,...,int_ptr,doub_ptr);

但是在MS Visual Studio 2008（Windows Vista）上构建之后运行此操作会导致运行时错误如上所述，

But running this after building on MS Visual Studio 2008 (Windows Vista), leads to run-time error as mentioned above, viz.,

在Linux上还没有测试过，我确定要避免将向量的内容复制到一个数组中。任何想法是怎么回事？

Haven't tested this on Linux yet and I sure would like to avoid copying the contents of the vector into an array just for this. Any ideas what is going on?

进一步编辑以确认使用Nick和Chris的推荐，并继续与Vlad等人进行讨论;这里是一个代码片段：

Further edit to confirm usage of Nick and Chris' recommendation and to continue discussion with Vlad et al; here's a code snippet:

#include <iostream>
#include <vector>

int main() {
   for(int i=2; i<6; ++i) {
      int isq = i*i;
      std::vector<int> v;
      v.reserve(4);
      for(int j=0; j<isq; ++j) {
         v.push_back(j);
      }
      std::cout << "Vector v: size = " << v.size() << " capacity = " << v.capacity()
                << "\n";
      std::cout << "Elements: \n";
      for(int k=0; k<v.size(); ++k) {
         std::cout << v.at(k) << "  ";
      }
      std::cout << "\n\n";
   }
   return 0;
}

提供输出：

Vector v: size = 4 capacity = 4
Elements:
0  1  2  3

Vector v: size = 9 capacity = 16
Elements:
0  1  2  3  4  5  6  7  8

Vector v: size = 16 capacity = 16
Elements:
0  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15

Vector v: size = 25 capacity = 32
Elements:
0  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21
22  23  24

推荐答案

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std::vector<int> vec_ints;
vec_ints.reserve(27);
std::vector<double> vec_doub;
vec_doub.reserve(27);
for(int i = 0; i < n; ++i) {
    vec_ints.push_back(...);
    vec_doub.push_back(...);
}
const int* int_ptr = &vec_ints[0];
const double* doub_ptr = &vec_doub[0];
func(...,...,int_ptr,doub_ptr);

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