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c - 无法将值从一个 double 复制到另一个 double 并且变量重置为0

我遇到的问题是我正在尝试比较2个数字。我将hGpa初始化为char'0.0'。读取文件时，它将获得gpa值并将其与hGpa进行比较。如果较高，则将其值分配给hGpa。该计划的重点是获得最高GPA。我的问题是值hGpa永远不会改变。我不确定是否分配错误或将变量放置在错误的位置，并且它们会不断被覆盖。我也不熟悉C，因此如果这是一个愚蠢的错误，我深表歉意。这是我的代码

我已经尝试过使这些值成为全局值，但是它们只是一直重置为0.0000。

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


#define MAXCHAR 1000
int main(void){



  FILE *fp;                 //pointer to file
  char *filename;           //pointer to name of file
  char *fileNames[] = {"CSCI4060U_Lab02_data/1.csv", "CSCI4060U_Lab02_data/2.csv",
                       "CSCI4060U_Lab02_data/3.csv", "CSCI4060U_Lab02_data/4.csv",
                       "CSCI4060U_Lab02_data/5.csv", "CSCI4060U_Lab02_data/6.csv",
                       "CSCI4060U_Lab02_data/7.csv"};
  long fileSize;

  int s = sizeof(fileNames) /sizeof(char*); //array consists of 8 char pointers
                                            //each char consists of 8 bytes in memory
                                            //so you get 64 / 8 = 8;



  for(int i = 0                             ; i < sizeof(fileNames)/sizeof(char*); i++){

    printf("Reading from file #%d: %s\n", i+1, fileNames[i] );
    fp = fopen(fileNames[i],"r");
    if(fp == NULL){
      printf("Could not open file %s",fileNames[i]);
      return 1;
    }
    fileSize = ftell(fp);
    char line[MAXCHAR];

    char hFirst = "";
    char hLast = "";
    char hGpa = "0.0";

    while(fgets(line, MAXCHAR, fp) != NULL){
      //printf("%s\n",line);

      char* first = strtok(line, ",");
      char* last = strtok(NULL, ",");
      char* gpa = strtok(NULL,",");

      printf("current highest: %s, %s, %s\n", hFirst, hLast, hGpa);


      double numGpa = atof(gpa);
      double numHGpa = atof(hGpa);

      printf("gpa read: %f ++++++ gpa current: %f\n",numGpa, numHGpa );

      if(&numGpa > &numHGpa){

        hFirst = first;
        hLast = last;
        hGpa = gpa;
        //printf("after assignment: %s, %s, %s\n", hFirst, hLast, hGpa);
      }



    }
    fclose(fp);

  }

  return 0;
}
    fclose(fp);


我阅读的示例文件如下：

Jesse,Jordan,0.65
Charles,Austin,3.23
Peter,Cole,1.57
David,Hamilton,2.73


基本上，它应该输入两次if语句并更改hGpa指向的值。再次对不起，如果我犯了任何愚蠢的明显错误。

最佳答案

有一次我给出了由编译器生成的消息：

pi@raspberrypi:/tmp $ gcc -pedantic -Wall c.c
c.c: In function ‘main’:
c.c:37:19: warning: initialization makes integer from pointer without a cast [-Wint-conversion]
     char hFirst = "";
                   ^~
c.c:38:18: warning: initialization makes integer from pointer without a cast [-Wint-conversion]
     char hLast = "";
                  ^~
c.c:39:17: warning: initialization makes integer from pointer without a cast [-Wint-conversion]
     char hGpa = "0.0";
                 ^~~~~
c.c:48:33: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘int’ [-Wformat=]
       printf("current highest: %s, %s, %s\n", hFirst, hLast, hGpa);
                                 ^
c.c:48:37: warning: format ‘%s’ expects argument of type ‘char *’, but argument 3 has type ‘int’ [-Wformat=]
       printf("current highest: %s, %s, %s\n", hFirst, hLast, hGpa);
                                     ^
c.c:48:41: warning: format ‘%s’ expects argument of type ‘char *’, but argument 4 has type ‘int’ [-Wformat=]
       printf("current highest: %s, %s, %s\n", hFirst, hLast, hGpa);
                                         ^
c.c:52:29: warning: passing argument 1 of ‘atof’ makes pointer from integer without a cast [-Wint-conversion]
       double numHGpa = atof(hGpa);
                             ^~~~
In file included from c.c:2:0:
/usr/include/stdlib.h:105:15: note: expected ‘const char *’ but argument is of type ‘char’
 extern double atof (const char *__nptr)
               ^~~~
c.c:58:16: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
         hFirst = first;
                ^
c.c:59:15: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
         hLast = last;
               ^
c.c:60:14: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
         hGpa = gpa;
              ^
c.c:20:7: warning: unused variable ‘s’ [-Wunused-variable]
   int s = sizeof(fileNames) /sizeof(char*); //array consists of 8 char pointers
       ^
c.c:18:8: warning: variable ‘fileSize’ set but not used [-Wunused-but-set-variable]
   long fileSize;
        ^~~~~~~~
c.c:13:9: warning: unused variable ‘filename’ [-Wunused-variable]
   char *filename;           //pointer to name of file
         ^~~~~~~~
c.c: At top level:
c.c:73:5: warning: data definition has no type or storage class
     fclose(fp);
     ^~~~~~
c.c:73:5: warning: type defaults to ‘int’ in declaration of ‘fclose’ [-Wimplicit-int]
c.c:73:5: warning: parameter names (without types) in function declaration
pi@raspberrypi:/tmp $


所以

char hFirst = "";
char hLast = "";
char hGpa = "0.0";


可

char * hFirst = "";
char * hLast = "";
char * hGpa = "0.0";


可以删除long fileSize;和fileSize = ftell(fp)

可以删除int s = sizeof(fileNames) /sizeof(char*);

可以删除char *filename;

最后的fclose(fp);必须删除

如您所见，仅询问警告并加以查看即可消除程序中的许多错误。



当然，编译器无法检查语义

if(&numGpa > &numHGpa){可能不是您想要的，可以是if(numGpa > numHGpa){

如果我放

Jesse,Jordan,0.65
Charles,Austin,3.23
Peter,Cole,1.57
David,Hamilton,2.73


在一个文件中，我将fileNames更改为只有它，执行为：

pi@raspberrypi:/tmp $ ./a.out
Reading from file #1: in.csv
current highest: , , 0.0
gpa read: 0.650000 ++++++ gpa current: 0.000000
current highest: Charles, s, n
gpa read: 3.230000 ++++++ gpa current: 0.000000
current highest: Peter, le,

gpa read: 1.570000 ++++++ gpa current: 0.000000
current highest: David, Hamilton, ton
gpa read: 2.730000 ++++++ gpa current: 0.000000


名称不正确，这是因为在将它们保存到hFirst，hLast和hGpa中的同时始终使用line读取和strtok时，您不会复制strtok的结果

所以一种可能性就是改变

char * hFirst = "";
char * hLast = "";
char * hGpa = "0.0";
...
hFirst = first;
hLast = last;
hGpa = gpa;


创建人：

char * hFirst = strdup("");;
char * hLast = strdup("");
char * hGpa = strdup("0.0");
...
free(hFirst);
free(hLast);
free(hGpa);
hFirst = strdup(first);
hLast = strdup(last);
hGpa = strdup(gpa);


由于printf("current highest: %s, %s, %s\n", hFirst, hLast, hGpa);，我使用strdup（“”）等进行了初始化

为避免内存泄漏更改

fclose(fp);


通过

fclose(fp);
free(hFirst);
free(hLast);
free(hGpa);


现在执行：

pi@raspberrypi:/tmp $ ./a.out
Reading from file #1: in.csv
current highest: , , 0.0
gpa read: 0.650000 ++++++ gpa current: 0.000000
current highest: Jesse, Jordan, 0.65

gpa read: 3.230000 ++++++ gpa current: 0.650000
current highest: Charles, Austin, 3.23

gpa read: 1.570000 ++++++ gpa current: 3.230000
current highest: Charles, Austin, 3.23

gpa read: 2.730000 ++++++ gpa current: 3.230000


在valgrind下：

pi@raspberrypi:/tmp $ valgrind ./a.out
==5547== Memcheck, a memory error detector
==5547== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==5547== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==5547== Command: ./a.out
==5547==
Reading from file #1: in.csv
current highest: , , 0.0
gpa read: 0.650000 ++++++ gpa current: 0.000000
current highest: Jesse, Jordan, 0.65

gpa read: 3.230000 ++++++ gpa current: 0.650000
current highest: Charles, Austin, 3.23

gpa read: 1.570000 ++++++ gpa current: 3.230000
current highest: Charles, Austin, 3.23

gpa read: 2.730000 ++++++ gpa current: 3.230000
==5547==
==5547== HEAP SUMMARY:
==5547==     in use at exit: 0 bytes in 0 blocks
==5547==   total heap usage: 12 allocs, 12 frees, 5,518 bytes allocated
==5547==
==5547== All heap blocks were freed -- no leaks are possible
==5547==
==5547== For counts of detected and suppressed errors, rerun with: -v
==5547== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 3)

关于c - 无法将值从一个 double 复制到另一个 double 并且变量重置为0，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/54560302/

10-09 13:26
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