1

I'm trying to save a dynamic array to a file but I'm having some issues. This is my current code:

/*********************************************************************
*
* 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;
}

I'll explain my program. It uses a NI USB 6211 to measure inputs and outputs, and then displays it. This program is used to measure the amount of voltage coming into the ADC. It reads it just fine and my dynamic array also works as it should. Now, when it comes down to the actual writing the file:

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

I'm getting the error "Null pointer was passed for a required parameter". Now, I KNOW this is coming from my fwrite code block, but i've tried so many different ways of writing the code, but it just doesn't want to comply. I've tried using pointers and also not, it just won't write the data. (When I say data, I mean the voltage reading).

4

3 回答 3

3

这个：

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

大声尖叫着“破密码”。注意类型的不匹配，假设float64大小相同，int听起来很危险。

它应该是：

i_array = malloc(j * sizeof *i_array);
  1. 不要强制转换malloc()in C的返回值。
  2. 不要重复类型，使用sizeof目标指针将类型“锁定”在一起。

此外，您应该始终检查是否malloc()成功，如果j有一个无意义的值，它将失败。

于 2013-08-20T08:57:03.667 回答
2

初始化i_array = (float64*) malloc (j * sizeof (int))时有两个问题：

  1. j未初始化。它有一个垃圾值。当你乘以它时，sizeof (int)你就是在乘以垃圾。这将导致内存分配产生未定义的结果。您需要先阅读，然后使用而不是作为乘数amount进行初始化。amountj
  2. 您已声明i_array为指向float64. 在这种情况下，您的数组元素需要是float64，而不是int。

所以：amount从输入中获取之后，分配你的数组：

i_array = malloc (amount * sizeof (float64));

有几件事：首先，转换 ; 的返回值被认为是非 C 类的malloc。其次，不要使用gets，从 C11 开始它是非标准的。改用fgets：

fgets (filename, sizeof (filename), stdin);
于 2013-08-20T09:03:07.383 回答
1

我认为你的问题是你没有初始化 j

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

所以这实际上是

i_array = (float64*)malloc(0);

一旦知道要像这样循环多少次，请尝试初始化数组：

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.");
}

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

for (j = 0; j < amount; j++)
{
    //...
于 2013-08-20T08:46:00.293 回答