c - fwrite() 动态数组到文件

Question

我正在尝试将动态数组保存到文件中，但遇到了一些问题。这是我当前的代码:

/*********************************************************************
*
* ANSI C Example program:
*    Acq-IntClk.c
*
* Example Category:
*    AI
*
* Description:
*    This example demonstrates how to acquire a finite amount of data
*    using the DAQ device's internal clock.
*
* Instructions for Running:
*    1. Select the physical channel to correspond to where your
*       signal is input on the DAQ device.
*    2. Enter the minimum and maximum voltages.
*    Note: For better accuracy try to match the input range to the
*          expected voltage level of the measured signal.
*    3. Select the number of samples to acquire.
*    4. Set the rate of the acquisition.
*    Note: The rate should be AT LEAST twice as fast as the maximum
*          frequency component of the signal being acquired.
*
* Steps:
*    1. Create a task.
*    2. Create an analog input voltage channel.
*    3. Set the rate for the sample clock. Additionally, define the
*       sample mode to be finite and set the number of samples to be
*       acquired per channel.
*    4. Call the Start function to start the acquisition.
*    5. Read all of the waveform data.
*    6. Call the Clear Task function to clear the task.
*    7. Display an error if any.
*
* I/O Connections Overview:
*    Make sure your signal input terminal matches the Physical
*    Channel I/O Control. For further connection information, refer
*    to your hardware reference manual.
*
*********************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <NIDAQmx.h>
#include <string.h>
#include <windows.h>


#define DAQmxErrChk(functionCall) if( DAQmxFailed(error=(functionCall)) ) goto Error; else
FILE *save_file = NULL;

int main(void)
{
    int32       error=0;
    int32       amount; 
    int32       counter[2]={'0'};
    TaskHandle  taskHandle=0;
    int32       read;
    float64*    i_array;
    int         j;
    char        errBuff[2048]={'\0'};
    char        c = 64;
    char        filename[256];

    char        answer[2];
    const int       ia=0;
    const char      a = 0;

    i_array = (float64*)malloc(j*sizeof(int));

    /*********************************************/
    // DAQmx Configure Code
    /*********************************************/

    printf("Please enter the amount of voltage checks you wish to run.\n");

    while(scanf("%d%c", &amount, &c) !=2) // This is where the user inputs his data. If it isn't a number, it returns false and goes into the while loop.
    {
        getchar();
        puts("Please enter a number.");
    }
    for (j = 0; j < amount; j++) // Loops through the specified amount
    {
        DAQmxErrChk (DAQmxCreateTask("",&taskHandle));
        DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandle,"Dev1/ai0","",DAQmx_Val_Cfg_Default,1.0,10.0,DAQmx_Val_Volts,NULL));
        DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandle,"",10000.0,DAQmx_Val_Rising,DAQmx_Val_FiniteSamps,1000));

        /*********************************************/
        // DAQmx Start Code
        /*********************************************/
        DAQmxErrChk (DAQmxStartTask(taskHandle));

        /*********************************************/
        // DAQmx Read Code
        /*********************************************/

        DAQmxErrChk (DAQmxReadAnalogF64(taskHandle,1000,10.0,DAQmx_Val_GroupByChannel,i_array,1000,&read,NULL));

        printf("Updating... ");
        printf("Data point %d has %f",j, i_array[j]); // Displays the voltage set number of times
        printf(" volts\n");
        Sleep(200); // ms pause between each reading

        if( taskHandle!=0 )
        {
            /*********************************************/
            // DAQmx Stop Code
            /*********************************************/
            DAQmxStopTask(taskHandle);
            DAQmxClearTask(taskHandle);
        }
    }

    if(j==amount)
    {
        printf("\nVoltage readings aquired. Please specify a filename so the data can be saved.\n");
        goto Save;
    }


Save:
    printf("\nPlease enter a filename...\n");
    gets(filename);
    printf("Name is: ");
    puts(filename);
    save_file = fopen(filename,"w");
    printf("File made");

        for (j = 0; j < amount; j++)
        {           
            fwrite(&i_array[j], sizeof(j), j, save_file);
                    printf("Saving...\nSaved.");
        }       

    getchar();
    free((void*) i_array);
Error:
    if( DAQmxFailed(error) )
        DAQmxGetExtendedErrorInfo(errBuff,2048);    

    if( DAQmxFailed(error) )                
        printf("DAQmx Error: %s\n",errBuff);

    return 0;
}

我会解释我的程序。它使用 NI USB 6211 测量输入和输出，然后显示出来。该程序用于测量进入 ADC 的电压量。它读起来很好，我的动态数组也能正常工作。现在，当涉及到实际写入文件时:

for (j = 0; j < amount; j++)
{           
    fwrite(&i_array[j], sizeof(j), j, save_file);
    printf("Saving...\nSaved.");
}

我收到错误消息“为所需参数传递了空指针”。现在，我知道这是来 self 的 fwrite 代码块，但我已经尝试了很多不同的代码编写方式，但它就是不想遵守。我试过使用指针，但也没有，它只是不会写入数据。 (当我说数据时，我指的是电压读数)。

Answer 1

这个:

i_array = (float64*)malloc(j*sizeof(int));

非常大声地尖叫“损坏的代码”。注意类型不匹配，假设 float64 与 int 大小相同听起来非常危险。

应该是:

i_array = malloc(j * sizeof *i_array);

1. Don't cast the return value of malloc() in C .
2. 不要重复类型，在目标指针上使用 sizeof 将类型“锁定”在一起。

此外，您应该始终检查 malloc() 是否成功，如果 j 具有无意义的值，它将失败。