C和C++开辟指针数组读取文件的测试

最新推荐文章于 2022-12-26 15:03:01 发布

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#c语言 #指针 #数组

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本文介绍了一个使用C++进行文件读取的例子，并展示了如何为不同类型的数组分配内存，包括一维数组和二维数组。通过多次读取同一文件并比较不同数据类型之间的区别，演示了文件操作的具体实现。

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

int main(void) {

const int Nu=5,Nv=5;

FILE *fp;
char filename[500];

long int nLen;
nLen=(Nu)*(Nv);

double *P=(double *)malloc(nLen*sizeof(double));

double *Q= new double[nLen];

double *(*R) = new double *[Nu];
for(int i = 0; i < Nu; ++ i)
R[i] = new double[Nv];

/********/
sprintf(filename,"MyData.dat");
if((fp=fopen(filename,"rb"))==NULL)
{
printf("cannot find the projection file\n");
exit(0);
}
for (int ii=0;ii<nLen;ii++)
fread(&P[ii],sizeof(double),1,fp);
fclose(fp);

/*******/

sprintf(filename,"MyData.dat");
if((fp=fopen(filename,"rb"))==NULL)
{
printf("cannot find the projection file\n");
exit(0);
}
fread(P,sizeof(double)*nLen,1,fp);
fclose(fp);

/********/

sprintf(filename,"MyData.dat");
if((fp=fopen(filename,"rb"))==NULL)
{
printf("cannot find the projection file\n");
exit(0);
}
for (int ii=0;ii<nLen;ii++)
fread(&Q[ii],sizeof(double),1,fp);
fclose(fp);


/********/
sprintf(filename,"MyData.dat");
if((fp=fopen(filename,"rb"))==NULL)
{
printf("cannot find the projection file\n");
exit(0);
}
for (int i=0;i<Nu;i++)
{
for (int j=0;j<Nv;j++)
fread(&R[i][j],sizeof(double),1,fp);
}
fclose(fp);

/********/



for (int i=0;i<Nu;i++)
{
for (int j=0;j<Nv;j++)
printf("%f ",P[i*Nv+j]);
printf("\n");
}


for (int i=0;i<Nu;i++)
{
for (int j=0;j<Nv;j++)
printf("%f ",R[i][j]);
printf("\n");
}

free(P);
delete Q;
delete []R;


}