Question

我尝试在文件中写入一些向量，但是atof函数给我带来了问题，我不知道如何解决。直到fscanf行（读为“％s％s \ n”，s1，s2）；它不会给我带来问题，然后是。



#include<iostream> 
#include<fstream> 
#include<string>
#include<stdlib.h>
#include <string.h>
#include <stdio.h>
#include<iomanip> 
#include<cmath>
using namespace std;

FILE *write,*read;

   double dz, pm ,xm, doub1,doub2;

   char s1[10],pz[10], s2[10],x[10], z[10];
int main(){
dz=0.00375;
   leer=fopen("data.dat","r");
   escribir=fopen("exitdata.dat","w+");//Donde vamos a escribir

   for(int a=0; a<5; a++){
        for(int i=0; i<10; i++){
            fscanf( read,"%s  %s \n", s1, s2);

//here begins the problem

            doub1 = atof(s1);
            doub2 = atof(s2);
            z[i]=(doub1+1)*dz;
            pz[i]=doub2;

            fprintf(escribir,"%s %s \n", s1,s2);
            cout<<z<<" "<<pz<<endl;


        }

        }

   fclose(escribir);//cerrar el archivo
   fclose(leer);


return 0;


}

Answer 1

atof函数运行得很好。

但是总的来说，您的代码中存在许多严重的问题。首先，也是最重要的：代码无法编译。编译器吐出许多错误。而且，它表明出了什么问题。因此，在发布有很多错误的代码之前，请运行编译器。

然后，我看到C ++标记-查看您的头文件。许多文件的末尾都有一个“ .h”。您正在使用语言C，但以下一行除外：cout << z << " " << pz << endl;。这也是错误的。它不会按照您的预期打印。

您在这里也没有使用任何向量。而且格式真的很糟糕。

首先让我进行简短的代码审查：

#include<iostream> 
#include<fstream>       // *** Not used 
#include<string>        // *** Not used 
#include<stdlib.h>      // *** Not used
#include <string.h>     // *** Not used
#include <stdio.h
#include<iomanip>       // *** Not used 
#include<cmath>         // *** Not used
using namespace std;

FILE* write, * read;    // *** Major bug. You are not using this variables, instead you are using 'leer' and 'escribir'

double dz, pm, xm, doub1, doub2;
// *** Do not use plain arrays in C++. Never
char s1[10], pz[10], s2[10], x[10], z[10]; // *** You want to be pz and z strings!

int main() {
    dz = 0.00375;
    // *** fopen is deprecated in C++
    leer = fopen("data.dat", "r");       // *** Major bug. Variable leer has not been defined
    escribir = fopen("exitdata.dat", "w+");//Donde vamos a escribir  // *** Do not write spanish// *** Major bug. Variable escribir has not been defined

    for (int a = 0; a < 5; a++) {        // *** Why 2 loops? And "a" is never used. Maybe you wan to read 5 values?
        for (int i = 0; i < 10; i++) {   // *** Why this loop? You want to copy data in the char array.
                                         // *** You are now invoking the loop body 50times
            // *** fscanf is deprecated in C++
            fscanf(read, "%s  %s \n", s1, s2); // *** Read is a none initialize variabel System will crash.You opened leer

            //here begins the problem    // ** no, the problem began with trying fscanf on a none initialize file pointer

            doub1 = atof(s1);
            doub2 = atof(s2);
            z[i] = (doub1 + 1) * dz;  // Complier error. You are trying to assign a double to 1 char
            pz[i] = doub2;            // Complier error. You are trying to assign a double to 1 char

            fprintf(escribir, "%s %s \n", s1, s2);
            cout << z << " " << pz << endl;   // *** Will output nothing. You are passing an empty char[]


        }

    }

    fclose(escribir);//cerrar el archivo
    fclose(leer);


    return 0;


}

如此之多的错误和对C和C ++的错误理解。让我使代码可编译。但是它仍然无法满足您的期望，因为您有大量的语义错误。

与MS Visual Studio 2019一起编译

#include<iostream> 
#include <stdio.h>

FILE* write, *read;

double dz, pm, xm, doub1, doub2;

char s1[10], pz[10], s2[10], x[10], z[10];

int main() 
{
    dz = 0.00375;
#pragma warning(suppress : 4996)
    read = fopen("r:\\data.dat", "r");
#pragma warning(suppress : 4996)
    write = fopen("r:\\exitdata.dat", "w+");

    for (int a = 0; a < 5; a++) {
        for (int i = 0; i < 10; i++) {
#pragma warning(suppress : 4996)
            fscanf(read, "%s  %s \n", s1, s2);
            doub1 = atof(s1);
            doub2 = atof(s2);
            //z[i] = (doub1 + 1) * dz; // No meaning
            //pz[i] = doub2;           // No meaning
            fprintf(write, "%s %s \n", s1, s2);
        }
    }
    fclose(write);
    fclose(read);
    return 0;
}

当然这也不能给您预期的结果。

最后是代码的C ++示例。请阅读一些不错的C ++书。请在cppreference中阅读有关使用的功能的信息。请尝试逐行了解。

#include <iostream>
#include <fstream>
#include <vector>
#include <iterator>
#include <algorithm>

struct TwoDoubles
{
    double doub1;
    double doub2;

    // Overwrite extractor  operator
    friend std::istream& operator >> (std::istream& is, TwoDoubles& td) {
        return is >> td.doub1 >> td.doub2;
    }
    // Overwrite inserter  operator
    friend std::ostream& operator << (std::ostream& os, const TwoDoubles& td) {
        return os << td.doub1 << ' ' << td.doub2;
    }
};

int main()
{
    // Open file with source data
    std::ifstream is("r:\\data.dat");

    // If file could be opened
    if (is) {

        // Open file containing results
        std::ofstream os("r:\\exitdata.dat");

        // If file could be opened
        if (os)
        {
            // Define a vector of doubles and initialize it
            std::vector<TwoDoubles> values{ std::istream_iterator<TwoDoubles>(is),std::istream_iterator<TwoDoubles>() };

            constexpr double dz = 0.00375;
            // Now we will calculate. Multiply all doubles with dz;
            std::for_each(values.begin(), values.end(), [dz](TwoDoubles & td) { td.doub1 = (td.doub1 + 1) * dz; });

            // Write everything to output file
            std::copy(values.begin(), values.end(), std::ostream_iterator<TwoDoubles>(os, "\n")) ;
        }
    }
    return 0;
}

请继续学习

为什么atof函数对我不起作用？ C ++

1 个答案: