结构中的向量不会让我 push_back [英] Vector in a struct wont let me push_back

问题描述

我在结构中有一个向量，用于 pthreads 参数传递:

Hi i have a vector in a struct as follows for pthreads argument passing:

struct thread_data{
   vector< pair < Database, string> > list_databases;
   ...
   ...
};

...some more code...

然后在稍后的函数中执行以下操作( mydata 是传递给函数的 thread_data )(条目是一对<数据库，字符串>)

then in a later function when i do the following ( mydata is a thread_data passed into the function ) ( entry being a pair< Database, string > )

mydata->list_databases.push_back(entry);

每当我这样做时，它都会告诉我 push_back 是非类类型.我不明白这个错误.我也尝试使用:

whenever I do this it tells me that push_back is of non-class type. I dont understand the error. I also tried using:

vector< pair<Database,string> > * list_databases;

和

mydata->list_databases->push_back(entry);

以及两者的结合.都给我同样的错误.任何人都可以提出建议吗?我已经研究过这个并且已经坚持了几个小时.谢谢

and a combination of the two. All give me the same error. Can anyone suggest something? I've researched this and have been stuck on it for hours. Thank you

其余代码如下:

#include<iostream>
#include<pthread.h>
#include<vector>
#include<string>
#include<fstream>

using namespace std;

struct thread_data{
   vector< pair<Database, string> >* list_databases;
   const char* store;
}

void* load_store( void* threadarg );

int main (){
  vector< pair <Database, string> > list;
  pthread_t thread1;
  string test;
  cout <<"$ ";
  cin >> test;

  const char* store_name = test.c_str();

  struct thread_data tester;
  tester.store = store_name;
  tester.list_databases = &list;

  pthread_create(&thread1,NULL,load_store, (void*) &tester);
  return 0;
}

void * load_store( void* threadarg ){
  struct thread_data *mydata;
  mydata = (struct thread_data*) threadarg;
  string store_used = mydata->store;

  ifstream load;
  string conversion;
  Database Loader;
  load.open(store_used.c_str());

  if(!load){ cerr << "Does not exist" << endl;
    exit(1);
  }

  while(!load.eof()){
    //...pushes file contents into database Loader...
  }
  load.close();
  pair < Database, string > new_store(Loader, store);
  mydata->list_databases->push_back(new_store);     // this is where the error occurs
 return 0;
}

推荐答案

mydata->list_databases.push_back(entry);，正如您在问题中所示，将失败，因为 thread_data::list_databases 是一个 vector<...>* 而不是 vector<...>.即，它是指针类型而不是类类型，正如您看到的编译器错误所指示的那样.

mydata->list_databases.push_back(entry);, as you've shown in your question, will fail because thread_data::list_databases is a vector<...>* rather than a vector<...>. I.e., it's a pointer-type rather than a class-type, just as the compiler error you're seeing indicates.

mydata->list_databases->push_back(new_store);，正如您在代码示例中所示，应该可以工作，只是您需要 #include ; 以便使用 std::pair.

mydata->list_databases->push_back(new_store);, as you've shown in your code sample, should work, except that you need to #include <utility> in order to use std::pair.

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