c - 为什么我的代码中出现段错误，您能解释一下按引用传递和按值传递吗？

Question

我正在用 C 编写程序。我正在尝试了解按引用传递和按值传递之间的区别。我不确定我是否做对了。

我在第二次执行 do while 循环后遇到段错误/核心转储错误。我在循环中遗漏了什么？

这是我的主要内容:

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

extern void CalculateTaxes(float gross,float defr, float *ft,float *st,float *ssit);
extern float calcGross(float hours, float payrate);
extern void InputEmplData(char *lastname, char *firstname, float *hours, float *payrate, float *defr);
extern void InitAcc(float *totreg, float *totovt, float *totrate, float *totgross, float *totfed, float *totstate, float *totssi, float *totdef,  float *totnet);
extern void AddDetail2Acc(float reghrs, float *totreg, float ovthrs, float *totovt, float pr, float *totpayrate, float theGross, float *totgross,float ft, float *totfed, float st, float *totstate, float ssit, float *totssi, float defr, float *totdef, float net, float *totnet);

int main(void)
{
   float fedtax,statetax,ssitax;
   float theGross;
   //int  counter=0;
   char answer;
   char lastname, firstname;
   float hours, payrate, defr, reghrs, ovthrs, net, numemps;
   float totgross, totpayrate, totreg, totovt, totrate, totfed, totstate, totssi, totdef, totnet;

/*
   FILE * reportFile; // 1) declare a FILE * variable

   reportFile = fopen("./report.txt","wt");
   // 2) open a report file with access mode "write-text"
   if (reportFile == NULL)
   {
     printf("  Report file open failed ...\n");
     fflush(stdin);
     getchar();
     exit(-10); // terminate w/ failure code -10; reqs <stdlib>
   }
*/
   printf("  Welcome to the Employee Tax Program\n");
   printf("  Please enter the number of employees taxes will be calculated:");
   scanf (" %f", numemps);
   InitAcc(&totreg, &totovt, &totrate, &totgross, &totfed, &totstate, &totssi, &totdef, &totnet);

   do 
   {
     InputEmplData(&lastname, &firstname, &hours, &payrate, &defr);   
     theGross = calcGross(hours, payrate); // call 3.4
     CalculateTaxes(theGross,defr,&fedtax,&statetax,&ssitax); // 3.5
     net=(theGross-defr)-fedtax-statetax-ssitax;
     AddDetail2Acc(reghrs, &totreg, ovthrs, &totovt, payrate, &totpayrate, theGross, &totgross,fedtax, &totfed, statetax, &totstate, ssitax, &totssi, defr, &totdef, net, &totnet);
     printf("    Fedtax    = %8.2f",fedtax);
     //fprintf(reportFile,"    Fedtax    = %8.2f",fedtax);
     //fprintf(stdout,"    Fedtax    = %8.2f",fedtax);
     printf("    Statetax  = %8.2f",statetax);
     //fprintf(reportFile,"    Statetax  = %8.2f",statetax);
     //fprintf(stdout,"    Statetax  = %8.2f",statetax);
     printf("    SSItax    = %8.2f\n",ssitax);
     //fprintf(reportFile,"    SSItax    = %8.2f\n",ssitax);
     //fprintf(stdout,"    SSItax    = %8.2f\n",ssitax);
     //printf(" %f %f %f %f %f %f %f %f", totreg, totovt, totrate, totfed, totstate, totssi, totdef, totnet);
     printf("  Do you have another employee(YES = 1 / No = 2) ==> ");
     fflush(stdin);
     scanf (" %c", answer);
     answer = getchar();
     getchar(); // removes '\n' from response

   } while (answer == 'y' || answer == 'y');

   //fclose(reportFile); // 4) close the file
   printf(" Press any key ... ");
   fflush(stdin);
   getchar();
   return 0;
}

这是我的功能:

#include <stdio.h>

void InputEmplData (char *lastname, char *firstname, float *hours, float *payrate, float *defr);

void InputEmplData (char *lastname, char *firstname, float *hours, float *payrate, float *defr)
{   
   printf("  Please enter your lastname: ");
   scanf (" %s", lastname);
   fflush(stdin);

   printf("  Please enter your firstname: ");
   scanf (" %s", firstname);
   fflush(stdin);

   printf("  Please enter the hours you have worked including overtime: ");
   scanf (" %f", hours);
   while (hours < 0)
   {
    printf(" Please enter a valid number. Must be between 0.");
    scanf (" %f", hours);
   }
   printf("  Please enter your payrate(15.00): ");
   scanf (" %f", payrate);
   while (payrate <= 0)
   {
    printf(" Please enter a valid number. Must be above 0.");
    scanf (" %f", payrate);
   }
   printf("  Please enter the amount exempt from taxes: ");
   scanf (" %f", defr);

   while (defr <= 0)
   {
    printf(" Please enter a valid number. Must be above 0.");
    scanf (" %f", defr);
   }
}

CalculateTaxes 函数:

#include "./taxrates.h" //user defined header for tax rates

void CalculateTaxes(float gross,float defr, float *ft,float *st,float *ssit);
float calcFed(float gross, float defr);
float calcState(float ft);
float calcSSI(float gross,float defr);

void CalculateTaxes(float gross,float defr, float *ft,float *st,float *ssit)
{
  *ft = calcFed(gross,defr);
  *st = calcState(*ft);
  *ssit = calcSSI(gross,defr);
}

float calcFed(float gross, float defr)
{
  return (gross-defr)*FEDTAXRATE;
}

float calcState(float ft)
{
  return ft * STATETAXRATE;
}

float calcSSI(float gross,float defr)
{
  return (gross-defr)*SSITAXRATE;
}


float calcGross(float h, float pr);

float calcGross(float h, float pr) 
{
  return h <= 40? h * pr : 40 *h + (h-40)*1.5*pr;
}

初始化计数器的函数:

void InitAcc(float *totreg, float *totovt, float *totrate, float *totgross, float *totfed, float *totstate, float *totssi, float *totdef,  float *totnet);

void InitAcc(float *totreg, float *totovt, float *totrate, float *totgross, float *totfed, float *totstate, float *totssi, float *totdef, float *totnet)
{
  *totreg = 0;
  *totovt = 0;
  *totrate = 0;
  *totgross = 0;
  *totfed = 0;
  *totstate = 0;
  *totssi = 0;
  *totdef = 0;
  *totnet = 0;
}

使用计数器的函数(未完成):

#include <stdio.h>

 void AddDetail2Acc(float reghrs, float *totreg, float ovthrs, float *totovt, 
            float pr, float *totpayrate, float theGross, float *totgross,
            float ft, float *totfed, float st, float *totstate, float ssit, float *totssi, 
            float defr, float *totdef, float net, float *totnet);

 void AddDetail2Acc(float reghrs, float *totreg, float ovthrs, float *totovt, 
            float pr, float *totpayrate, float theGross, float *totgross,
            float ft, float *totfed, float st, float *totstate, float ssit, float *totssi, 
            float defr, float *totdef, float net, float *totnet)
{
    *totgross+= theGross;
    *totreg += reghrs;
    *totovt += ovthrs;
    *totpayrate += pr;
    *totfed += ft;
    *totstate += st;
    *totssi += ssit;
    *totdef += defr;
    *totnet += net;

}

生成文件:

calc.obj:   calctaxes.cpp taxrates.h
    g++ -c calctaxes.cpp -o calc.obj

main2.exe:  main2.cpp calc.obj cGross.obj InputEmplData.obj InitAcc.obj
    g++ main2.cpp calc.obj cGross.obj InputEmplData.obj InitAcc.obj AddDetail2Acc.obj -o main2.exe

cGross.obj: calcGross.cpp InputEmplData.obj
    g++ -c calcGross.cpp -o cGross.obj

InputEmplData.obj:  InputEmplData.cpp
    g++ -c InputEmplData.cpp -o InputEmplData.obj

InitAcc.obj:    InitAcc.cpp InputEmplData.obj
    g++ -c InitAcc.cpp InputEmplData.obj -o InitAcc.obj

AddDetail2Acc.obj:  AddDetail2Acc.cpp
    g++ -c AddDetail2Acc.cpp InitAcc.obj -o AddDetail2Acc.obj

Answer 1

这里确实有很多代码，但这是我看到的第一个错误:

//...
extern void InputEmplData(char *lastname, char *firstname, float *hours, float *payrate, float *defr);
//...

    char lastname, firstname;

//...
    InputEmplData(&lastname, &firstname, &hours, &payrate, &defr);

//...
void InputEmplData (char *lastname, char *firstname, float *hours, float *payrate, float *defr)
{   
   printf("  Please enter your lastname: ");
   scanf (" %s", lastname);
   fflush(stdin);

   printf("  Please enter your firstname: ");
   scanf (" %s", firstname);
   fflush(stdin);

除非您不假设 lastname 和 firstname 的长度为 1，否则这是您的第一个错误。您正在接收段错误，因为您正在将长度大于 1 的字符串写入 char。

可能的更正是定义:

char lastname[NAME_LENGTH], firstname[NAME_LENGTH];

/...
InputEmplData(lastname, firstname, &hours, &payrate, &defr);

有了这个，您将达到预期的效果。我为 lastname 和 firstname 使用了 char 数组，但是您可以使用 malloc 为 lastname 等动态分配内存，但我不建议您在不清楚自己在做什么的情况下这样做。

此外，我只有几个小建议，没有考虑段错误:

1.尝试创建一些结构，以表示不同的变量组。然后你可以写，例如，而不是

void AddDetail2Acc(float reghrs, float *totreg, float ovthrs, float *totovt, 
            float pr, float *totpayrate, float theGross, float *totgross,
            float ft, float *totfed, float st, float *totstate, float ssit, float *totssi, 
            float defr, float *totdef, float net, float *totnet);

像这样:

void AddDetail2Acc(AccStruct *in_out_sourceAcc, AddDataStruct in_addData);

这更具可读性且不易出错。

2.据我所知，您正在使用货币值执行一些操作的变量名称。尽量不要使用 float 变量来表示货币值。 Floating point arithmetic有一天可以给你一个小小的惊喜。尝试使用整数类型。