如何读取存储在二进制文件中的数组或变量，并在程序中打印出来？

Question

我无法从用另一个 c 程序编写的文件中获取变量/元素的值以存储到正在运行的 c 程序的变量/元素中。 在将变量“i”读入程序（这是一个已经确定并存储在文件“inventory.txt”中的整数）时，我不断收到分段错误。 “i”表示正在打印的数组的元素数量（大小）。这是损坏的代码）：。

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

int main()
{
    int l, k;
    int *pn, *arraysize, *q;
    float *p;
    FILE *fp = fopen( "inventory.txt", "r+b" ); //declarations and I open up the binary file "inventory.txt"

    if ( fp == NULL )
    {                           //check file
        printf( "nah" );
        exit( EXIT_FAILURE );
    }

    *arraysize = fread( &arraysize, sizeof( int ), 1, fp );     //set arraysize in this program equal to i in the binary file inventory.txt?????? Here is where I get segmentation fault

    printf( "marker1" );        //place marker, I am not getting to this point when running the program

    for ( l = 0; l < *arraysize; l++ )
    {
        q[l] = fread( &q[l], sizeof( int ), arraysize, fp );    //set array elements ("arraysize" of them) pn, q, and p to the array elements of the same name in binary file inventory.txt
        p[l] = fread( &p[l], sizeof( int ), arraysize, fp );
        pn[l] = fread( &pn[l], sizeof( int ), arraysize, fp );
    }

    printf( "Below are the items in your inventory.\nPart#\tQuantity\tPrice\n" );       //print out the values
    for ( l = 0; l < *arraysize; l++ )
    {
        printf( "%5d\t", pn[l] );
        printf( "%8d\t", q[l] );
        printf( "%9.2f\n", p[l] );
    }
    return 0;
}

Answer 1

下面是你的一些代码：

int *arraysize;
*arraysize=fread(&arraysize,sizeof(int),1,fp);

您将arraysize 声明为int *（一个指针），但随后您尝试将一个int 读入其中。这是没有意义的。然后您尝试取消引用它以存储返回值，该值崩溃，因为它不是有效的指针。

你可能想要

int arraysize;
if (fread(&arraysize, sizeof(int), 1, fp) != 1) {
    fprintf(stderr, "error reading file\n");
    exit(1); }

将arraysize 声明为一个简单的int（不是指针）并读入它。

您的其他 fread 调用也存在类似问题。

Answer 2

您的指针有点错误，代码从未分配任何内存来读取值，fread() 返回读取的项目数，代码（出于某种原因）用这个结果覆盖刚刚读取的值。

这是一个补丁版本，但您没有包含任何测试数据，因此未经测试。

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

int main(  )
{
    int    l;
    int   *pn;
    int   *q;
    float *p;
    int    arraysize;

    FILE *fp = fopen( "inventory.txt", "r+b" ); //declarations and I open up the binary file "inventory.txt"

    if ( fp == NULL )
    {                           //check file
        printf( "nah" );
        exit( EXIT_FAILURE );
    }

    fread( &arraysize, sizeof( int ), 1, fp );     //set arraysize in this program equal to i in the binary file inventory.txt?????? Here is where I get segmentation fault

    printf( "marker1" );        //place marker, I am not getting to this point when running the program


    // Allocate some memory to hold the data (Yes! With cast on malloc())
    q  = (int *)malloc(arraysize * sizeof( int ));  // TODO - check malloc() OK
    pn = (int *)malloc(arraysize * sizeof( int ));  // TODO - check malloc() OK
    p  = (float *)malloc(arraysize * sizeof( float ));  // TODO - check malloc() OK

    // read each entire block in a single operation
    fread( q, sizeof( int ), arraysize, fp );    //set array elements ("arraysize" of them) pn, q, and p to the array elements of the same name in binary file inventory.txt
    fread( p, sizeof( float ), arraysize, fp );
    fread( pn, sizeof( int ), arraysize, fp );


    printf( "Below are the items in your inventory.\nPart#\tQuantity\tPrice\n" );       //print out the values
    for ( l = 0; l < arraysize; l++ )
    {
        printf( "%5d\t", pn[l] );
        printf( "%8d\t", q[l] );
        printf( "%9.2f\n", p[l] );
    }
    return 0;
}