Question

这是指向错误消息图片的链接：

http://www.flickr.com/photos/76298377@N02/6798897020/in/photostream

这是实际的编程问题。这是第3号

http://books.google.com/books?id=bSy1hBCLNl8C&pg=PA335&lpg=PA335&dq=sales.dat+c%2B%2B&source=bl&ots=mmN9b4WzsN&sig=miAD8-u4ly8K1Mou9ZNHv90Nscc&hl=en&sa=X&ei=2wdQT_-4OtSCsgK-l5WyDg&ved=0CDcQ6AEwAg#v=onepage&q=sales.dat%20c%2B%2B&f=false

以及这里的源代码

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

using namespace std;

#define numItems     8
#define numSalesP   10

// the product prices 
float prices  [numItems] = {345.0,  853.0, 471.0, 933.0, 721.0, 663.0, 507.0, 259.00};

// the product numbers
int   prodNum [numItems] = {7,      8,     9,     10,    11,    12,    13,    14};

// the salespersons IDs
int   salesP  [numSalesP] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

// the output file pointers
FILE * filePtrs[numSalesP];

// sales totals for every salespersons
float totals  [numSalesP];

//get the product index from the prodNum array
int getProdIndex (int product) {
    int i;
    for (i=0; i< numItems; i++) {
        if (prodNum[i] == product) {
            return i;
        }
    }
    return -1;
}

// get a product price from the product index
float getProdPrice (int prodIndex) {
    return prices[prodIndex];
}

// open a salesperson output file
void openSalesPFiles () {
    int i;
    char fileName[16];;

    for (i=0; i<numSalesP; i++) {
        sprintf(fileName, "salespers%d.dat", i+1);
//DEBUG         cout << fileName << endl;
        filePtrs[i] = fopen(fileName, "r");
    }
}

// close Salespersons files
void closeSalesPFiles () {
    int i;
    for (i=0; i<numSalesP; i++) {
        fclose(filePtrs[i]);
    }
}

// get sales person index from its ID
int getSalesPIndex (int salesPerson) {
    int i;
    for (i=0; i< numSalesP; i++) {
        if (salesP[i] == salesPerson) {
            return i;
        }
    }
    return -1;
}



int main () {
    int i;                  // generic counter
    FILE * salesFile;       // the input file with all sales
    int salesPId;           // salesperson ID
    int salesPIndex;        // salesperson index in array
    int prodId;             // product ID
    int pIndex;             // product index in array
    int qty;                // quantity
    float total;            // total for one sale

    // open all salespersons output files
    openSalesPFiles();

    // open the input file
    salesFile = fopen("sales.dat", "r");

    // read all record in the input file
    while (!feof(salesFile)) {

        fscanf(salesFile, "%d %d %d", &salesPId, &prodId, &qty);
//DEBUG        cout << salesPId << " --- " << prodId << " --- " << qty << endl;

        // validate sales person
        salesPIndex = getSalesPIndex (salesPId);
        if (salesPIndex < 0) {
            cout << "Invalid Sales person ID " << salesPId << endl;
            continue;
        }

//DEBUG        cout << "Salesperson index : " << salesPIndex << endl;

        // validate product id
        pIndex = getProdIndex (prodId);
        if (pIndex < 0) {
            cout << "invalid product id : " << prodId << endl;
            fprintf(filePtrs[salesPIndex], "Invalid Product ID %d\n", prodId);
            continue;
        } 
        else {
            // compute the sale total
            total = qty * prices[pIndex];
//DEBUG            cout << "total : " << total << endl;;

            // add it to the totals for this salesperson
            totals[salesPIndex] += (qty * prices[pIndex]);

            // write the sale to the salesperson file
            fprintf(filePtrs[salesPIndex], "%d %d %2.2f\n", prodId, qty, total);
        }
    }

    // print totals in salespersons files
    for (i=0; i< numSalesP; i++) {
        fprintf(filePtrs[i], "Total Sales : %8.2f\n", totals[i]);
    }

    // close all files
    closeSalesPFiles();
    fclose(salesFile);


}

导致我出现此类错误的代码有什么问题？感谢：S

Answer 1

断言来自名为 feoferr.c 的文件。这表明它与feof函数有关。断言说它预期stream != NULL。断言失败，因此stream显然是空指针。由于feof采用文件流参数，因此可以安全地猜测断言消息提到的流是文件流参数。你可以这样打feof：

// open the input file
salesFile = fopen("sales.dat", "r");

// read all record in the input file
while (!feof(salesFile)) {

所以也许salesFile是一个空指针。如您所知，fopen无法打开文件时可能会发生这种情况。也许该文件不存在，或者您可能没有读取权限。

下次遇到错误时，请使用您面前的工具。你有一个调试器，它应该在程序失败时中断你的程序。它可以带您到失败的线或最接近它的线。这应该会在你打电话给fopen之后给你提示问题很快就会出现。开始在那里调查。

在代码之后的代码中设置断点，并查看在程序失败之前是否到达它们。如果你没有那么远，那么在发布问题时不要包含这些功能。不要使用大量不相关的代码来阻止潜在的帮助者进行筛选以解决真正的问题。

如果遇到问题，请确保您的函数返回您期望的值。如果您不知道期望他们返回什么，请阅读文档并进行一些实验。确保你理解你所写的所有代码。

C程序的Debug Assertion错误

1 个答案: