小编and*_*and的帖子

为什么Java的设计者认为它有用/必要？

调用vector时我得到这个编译器错误size().为什么？

#include <vector>
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <cassert>


using namespace std;

class Vertex {

    float firstValue;
    float secondValue;
    float thirdValue;

    Vertex (float first, float second, float third){
          firstValue=first;
          secondValue=second;
          thirdValue=third;
    }

};


int main()
{
    cout<<"This program loads a 3D .off object. \nEnter the name of the file that describes it "<<endl;
    string inputFileName;
    getline(cin, inputFileName);

    ifstream inputFileStream;

    inputFileStream.open(inputFileName.data());
    assert (inputFileStream.is_open());

    string actualLine;

    for(;;){

        inputFileStream>>actualLine;

        istringstream actualLineStream(actualLine);



        std::vector<float> results( std::istream_iterator<int>(actualLineStream)
                        , std::istream_iterator<int>() ); …

我有一个完整的ArrayList:

class TransitionState {

    Position positionA;
    Position positionB;

    int counter;

    public boolean equals (Object o){

        if (o instanceof TransitionState){

          TransitionState transitionState= (TransitionState)o;

          if ((this.positionA.equals(transitionState.positionA))
                  &&(this.positionB.equals(transitionState.positionB)))
          {
              return true;
          }
        }
     return false;

    }

    @Override
    public String toString() {

        String output = "Position A " + positionA.i+ " "+ positionA.j + " "+ positionA.orientation + " "+
                "Position B " + positionB.i + " "+ positionB.j + " "+ positionB.orientation;

        return output;
    }

}

class Position {

    int i;
    int j; …

string aux;
int maxy,auxx=0;

cin>>aux;

maxy= (int)sqrt(aux.size());

我在说:

1> error C2668: 'sqrt' : ambiguous call to overloaded function
1>        could be 'long double sqrt(long double)'
1>        or       'float sqrt(float)'
1>        or       'double sqrt(double)'

为什么？

a)在这种情况下,随机数发生器是否在每次运行时使用系统的时钟(进行种子更改)？

b)种子是否用于生成expovariate(lambda)的伪随机值？

我想做点什么

java -enableassertions com.geeksanonymous.TestClass

我该怎么做呢？

这个矩阵转置函数有效,但我试图理解它的逐步执行,我不明白.

    transpose:: [[a]]->[[a]]
    transpose ([]:_) = []
    transpose x = (map head x) : transpose (map tail x)

同

transpose [[1,2,3],[4,5,6],[7,8,9]]

它返回:

 [[1,4,7],[2,5,8],[3,6,9]]

我不知道连接运算符如何使用map.它是在同一函数调用中连接x的每个头？怎么样？

这是

(map head x)

创建每个列表的头元素列表？

编译此代码时,我得到:

致命错误C1083:无法打开包含文件:'fstream.h':没有这样的文件或目录

为什么？

码:

#include <windows.h>   // use as needed for your system

#include <gl/Gl.h>
#include <gl/glut.h>
#include <iostream>
#include <fstream.h>

//**************Global Data
char ifileName[30],oFileName[30];
fstream inFile,outFile;

//************ Data structure 
struct GLfloatPoint
{ GLfloat x,y;
};

const int MAX = 100;
class GLfloatPointArray
{
public:
  int num;
  GLfloatPoint pt[MAX];
};

//***************** subprograms
typedef GLfloat colorType[3];
// subprogram used to draw the control points separately
void drawDot (GLfloat x, GLfloat y, GLfloat r, GLfloat g, GLfloat b)
{ glColor3f(r,g,b);
  glBegin (GL_POINTS); …

我在Oracle SQL Developer上遇到以下错误:

Error starting at line 1 in command:
    ALTER TABLE AEROPUERTO ADD CONSTRAINT AEROPUERTO_FK FOREIGN KEY (CODIGO_CIUDAD) REFERENCES CIUDAD(CODIGO)

Error report:
    SQL Error: ORA-02298: cannot validate (SYSTEM.AEROPUERTO_FK) - parent keys not found
    02298. 00000 - "cannot validate (%s.%s) - parent keys not found"
    *Cause:    an alter table validating constraint failed because the table has
               child records.
    *Action:   Obvious

为什么？

对于我的OS类,我应该只使用系统调用来实现Linux的cat(没有printf)

阅读此参考,我发现它被用于打印到文件.我想我应该操纵游戏.

在示例中出现: ofstream outfile ("new.txt",ofstream::binary);

如何将其写入屏幕？

编辑:我意识到这个write()是iostream库的一部分,这是否与int write(int fd,char*buf,int size)系统调用相同？