警告 C4700:未初始化的局部变量

warning C4700: uninitialized local variable

本文关键字：局部变量 初始化 C4700 警告      更新时间：2023-10-16

当我编译时，它说"警告C4700：使用了未初始化的局部变量'count'"。我不知道它为什么这么说，我没有来这里，所以有人可以做我的功课。只是寻求有关此错误的帮助，我知道它与函数定义有关 ReadStudentData 或 Main 中。

谢谢

#include<iostream>
#include<fstream>
#include<string>
using namespace std;
struct StudentType
{string studentName;
int testScore;//Between 0 and 100
char grade;

}student[20];
void PrintNameHeader(ostream& out);
bool OpenInputFile(ifstream& inFile, string& infilename ); //OPEN input file
void Pause();// Pause
void ReadStudentData(ifstream& infile, StudentType student[], int& );// Read student infp including first and last name and test score
void AssignGrades(StudentType student[], int);//assign grades to each student
int HighestScore(const StudentType student[], int );//Get the highest scores
void PrintNamesWithHighestScore(const StudentType student[], int);//Print name with highest Scores
void DisplayAllStudents(const StudentType student[], int);//Display all students
void GetLowHighRangeValues(int& , int&);//for example a student types 50 100 , it will get all students within that range
void DisplayStudentsInRange(const StudentType student[], int, int, int);// display students in that range
void SortStudentsByName(StudentType student[], int);// sort students by name
void SortStudentsByScore(StudentType student[], int);// sort students by test score highest to lowest

const int NUM_STUDENTS = 20;
int main()
{
    ifstream infile;
    string inFilename;
    int count = 0;
    StudentType student[NUM_STUDENTS];
    int numStudents;

    PrintNameHeader(cout);
    OpenInputFile(infile,inFilename);
    ReadStudentData(infile, student, numStudents);
    AssignGrades(student, numStudents);
    return 0;
}
//Function definitions
void PrintNameHeader(ostream& out)
{
    //Display name header on screen
    cout << "name" << endl;

}
bool OpenInputFile(ifstream& inFile, string& infilename)
{

    cout << "Enter the name of the .txt file that you want to open for input.n";
    cout << "Do not put spaces in the file name ";
    cin >> infilename;
    cout << endl;

    inFile.open(infilename.c_str());
    if (inFile.fail())
    {
        cout << "Sorry, the input file " << infilename <<" was not found"<< endl;
            return false;   
    }
    cout << "Input file " << infilename << " is open for reading.nn";
    return true;     
}
void Pause()
{
    cout << endl;
    cin.ignore(80, 'n');
    cout<<"Please hit the enter key to continue...n";
    cin.get();
}
void ReadStudentData(ifstream& infile, StudentType student[], int& numstudents)
{
    string firstName,
        LastName,
        testScore;
    int count = 0;

    if( infile)
        for (int count; count < NUM_STUDENTS; count++)
        {
            cin >> firstName[count] >> LastName[count] >> testScore[count];
            student[count].studentName = firstName +  ", " + LastName;
        }


        numstudents = count;
        cout << numstudents << endl;


}
void AssignGrades(StudentType student[], int numstudents)
{
    int i;
    for(i=0;i< NUM_STUDENTS;i++)
        switch((int)(student[i].testScore/10))
    {case 10:
    case 9: student[i].grade='A';
        break;
    case 8: student[i].grade='B';
        break;
    case 7: student[i].grade='C';
        break;
    case 6: student[i].grade='D';
        break;
    default: student[i].grade='F';
        break;
    }
}
int HighestScore(const StudentType student[], int numstudents)
{
    int max=0,i;
    for(i=1;i<numstudents;i++)
    {
        if(student[i].testScore>student[max].testScore)
            max=i;
    }
    return max;
}
void PrintNamesWithHighestScore(const StudentType student[], int numstudents)
{
}
void DisplayAllStudents(const StudentType student[], int numstudents)
{
}
void GetLowHighRangeValues(int& lowRange, int& highRange)
{
}
void DisplayStudentsInRange(const StudentType student[], int numStudents, int lownum, int highNum)
{
}
void SortStudentsByName(StudentType student[], int numStudents)
{
}
void SortStudentsByScore(StudentType student[], int numstudents)
{
}

它指的是这个：

for (int count; count < NUM_STUDENTS; count++)
//   ^^^^^^^^^

您可能需要初始化count，大概是为了0：

for (int count = 0; count < NUM_STUDENTS; count++)

或者，也许您的意思是使用在外部块中声明的相同count：

for (; count < NUM_STUDENTS; count++)

在 for 中定义另一个未初始化的计数变量。 您应该在以下位置初始化它：

for (int count = 0; count < NUM_STUDENTS; count++)

或者，如果在外部范围内需要声明，请将其删除：

for (; count < NUM_STUDENTS; count++)

C 和 C++ 有两个不同的组件来准备要使用的变量/对象。声明和初始化。

这些是声明：

int i;
Object o;
struct Foo;

这些声明事物，它们不会告诉编译器它们应该从什么值开始。以下是合法的：

int meaning;
if (day == "Thursday")
    meaning = 42;
else
    meaning = 0;

此代码确保含义始终具有值。

不幸的是，在 C 和 C++ 基元类型（如 int 等）没有漂亮、安全的默认值。所以如果你写：

int meaning;
if (day == "Thursday")
    meaning = 42;
else if (day == "Friday")
    meaning = 0;

当一天是"星期一"时，"意义"的价值是什么？如果你想到一个数字，你就错了。答案是：它没有定义。

编译器将允许您构建这样的代码，但它将提供您看到的错误以帮助您保护自己。

要同时声明 AND 初始化变量，只需执行以下操作：

int meaning = 0;
if (day == "Thursday")
    meaning = 42;

在您的代码中，问题是这样的：

for (int count; count < NUM_STUDENTS; ++count)

这应该是

for (int count = 0; count < NUM_STUDENTS; ++count)

否则，程序可能会编译，但"count"的初始值可以是 -2^31 到 +2^31 之间的任何数字。

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