代码用途
该代码应模拟CPU调度算法。目前只写了FCFS（先到先得）和SJF（最短的工作先到）
问题
运行代码时，使用FCFS“路径”时收到以下错误
*** Error in `./test2': double free or corruption (!prev): 0x000055f54ecc7830 ***
从我在网上发现的内容来看，这与内存溢出问题有关，尽管在个人PC上运行此程序后，该路径没有出现错误。我已经检查了循环和数组减速度，但找不到问题。
我相信我的问题可能与以下for循环有关
//compare values in at to find earliest arrival time. Basically loops through dataset values and sorts them into the arrival order
for(i=0; i<processes; i++)
{
for(j=0; j<processes; j++)
{
if(at[i]<at[j]) //if the value of i is smaller than j (basically gets the smallest value in array)
{
temp=at[i]; //temp int equals arrival time of i
at[i]=at[j]; //arrival time i changes to value of arrival time j
at[j]=temp; //arrival time j becomes original value of arrival time i (basically switching the values of i and j)
temp=bt[i]; //temp becomes value of burst time i
bt[i]=bt[j]; //burst time i becomes values of burst time j
bt[j]=temp; //burst time j becomes the original value of burst time i (basically switching the values of i and j)
temp=pid[i]; //t changes to value of pid i
pid[i]=pid[j]; //pid i becomes value of pid j
pid[j]=temp; //pid j becomes value of t (basically switching the values of i and j)
}
}
}
我正在测试的主要数据集是数据集3，其中包含以下数据
PID AT BT
0 3 4
1 1 5
2 2 20
3 0 25
4 6 14
5 8 6
与该代码有关的所有文件都可以位于以下链接（我很抱歉，链接不是首选，但它是使用正确格式共享数据集的最简单方法）
完整代码
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char filename[100];
char *buffer = NULL;
int schedtoken;
char entries[10];
int fcfs()
{
int pid[10],at[10],bt[10],st[10],ft[10],tat[10],wt[10],i=0,j=0,processes=6,temp,n1,n2,n3;
int totwt=0,tottat=0;
char c1,c2,c3,fcfsselection;
printf("\n\n\nPlease select the dataset you would like to use\n\n");
printf(" 1. Dataset1\n 2. Dataset2\n 3. Dataset3\n 4. Quit\n\nSelection:\n");
scanf(" %c",&fcfsselection);
// Get data set user wants and amend filename based on selection
switch(fcfsselection)
{
case '1':
printf("\nYou have selected Dataset1\n");
strcpy(filename, "datasets/dataset1.txt");
break;
case '2':
printf("\nYou have selected Dataset2\n");
strcpy(filename, "datasets/dataset2.txt");
break;
case '3':
printf("\nYou have selected Dataset3\n");
strcpy(filename, "datasets/dataset3.txt");
break;
case '4':
printf("\nThank you for using this tool!");
break;
default:
printf("\nERROR!: Incorrect selection - Returning to Menu\n");
fcfs();
}
//Import dataset file, store the first line of char's (crashes if only checking for ints) and the rest of the ints
FILE *fp;
fp=fopen(filename,"r");
if (fp == NULL)
{
printf("Cannot open file at %s, try again.", filename);
fcfs();
}
else
{
fscanf(fp,"%s%s%s",&c1,&c2,&c3);
while(fscanf(fp,"%d%d%d",&n1,&n2,&n3)!=EOF)
{
pid[i]=n1;
at[i]=n2;
bt[i]=n3;
i++;
}
}
fclose(fp);
//compare values in arr time to find earliest arrival time. Basically loops through dataset values and sorts them into the arrival order
for(i=0; i<processes; i++)
{
for(j=0; j<processes; j++)
{
if(at[i]<at[j]) //if the value of i is smaller than j (basically gets the smallest value in array)
{
temp=at[i]; //temp int equals arrival time of i
at[i]=at[j]; //arrival time i changes to value of arrival time j
at[j]=temp; //arrival time j becomes original value of arrival time i (basically switching the values of i and j)
temp=bt[i]; //temp becomes value of burst time i
bt[i]=bt[j]; //burst time i becomes values of burst time j
bt[j]=temp; //burst time j becomes the original value of burst time i (basically switching the values of i and j)
temp=pid[i]; //t changes to value of pid i
pid[i]=pid[j]; //pid i becomes value of pid j
pid[j]=temp; //pid j becomes value of t (basically switching the values of i and j)
}
}
}
//complete calculations
for(i=0; i<processes; i++)
{
if(i==0)
st[i]=at[i]; //if i equals 0 (basically the beggining of the sim) then the start time equals the arrival time of the first entry (so 0)
else
st[i]=ft[i-1]; //otherwise the start value equals the finish value of the last entry run -1
wt[i]=st[i]-at[i]; //wait time equals the start time of the process minus the arrival time
ft[i]=st[i]+bt[i]; //finish time equals start time plus run time
tat[i]=ft[i]-at[i]; // turn around time equals finish time minus arrival time
}
tottat=0;
//print results
printf("\nPID\t AT\t BT\t WT\t ST\t TAT\t CT");
for(i=0; i<processes; i++)
{
printf("\n%3d\t%3d\t%3d\t%3d\t%3d\t%3d\t%3d",pid[i],at[i],bt[i],wt[i],st[i],tat[i],ft[i]);
totwt+=wt[i];
tottat+=tat[i];
}
printf("\n\nAverage Waiting Time:%f",(float)totwt/processes);
printf("\nAverage Turn Around Time:%f",(float)tottat/processes);
fclose(fp);
//Open new file to print output
FILE *f = fopen("datasets/output.txt", "w");
if (f == NULL)
{
printf("Error opening file!\n");
exit(1);
}
//Print output to file
fprintf(f, "PID\t AT\t BT\t WT\t ST\t TAT\t CT");
for(i=0; i<processes; i++)
{
fprintf(f,"\n%3d\t%3d\t%3d\t%3d\t%3d\t%3d\t%3d",pid[i],at[i],bt[i],wt[i],st[i],tat[i],ft[i]);
}
fprintf(f,"\n\nAverage Waiting Time:%f",(float)totwt/processes);
fprintf(f,"\nAverage Turn Around Time:%f",(float)tottat/processes);
printf("\n\nThe results for the dataset simulated are stored in: datasets/output.txt");
fclose(f);
return 0;
}
char* getfile(char *filename)
{
int string_size, read_size;
FILE *file = fopen(filename, "r");
if (file)
{
// Seek the last byte of the file
fseek(file, 0, SEEK_END);
// Offset from the first to the last byte, or in other words, filesize
string_size = ftell(file);
// go back to the start of the file
rewind(file);
// Allocate a string that can hold it all
buffer = (char*) malloc(sizeof(char) * (string_size + 1) );
// Read it all in one operation
read_size = fread(buffer, sizeof(char), string_size, file);
// fread doesn't set it so put a \0 in the last position
// and buffer is now officially a string
buffer[string_size] = '\0';
if (string_size != read_size)
{
// Something went wrong, throw away the memory and set
// the buffer to NULL
free(buffer);
buffer = NULL;
}
// Always remember to close the file.
fclose(file);
}
// printf("%s",buffer);
return buffer;
}
void schedintro(int schedtoken)
{
//take the value of schedtoken, change the value of filename to relavent file path and use getfile to open and then print the file. Call relavent scheduling function to do calculations
if(schedtoken==1)
{
strcpy(filename, "headers/fcfsheader.txt");
getfile(filename);
printf("%s",buffer);
fcfs();
}
else if(schedtoken==2)
{
strcpy(filename, "headers/sjfheader.txt");
getfile(filename);
printf("%s",buffer);
}
else if(schedtoken==3)
{
strcpy(filename, "headers/rrheader.txt");
getfile(filename);
printf("%s",buffer);
}
}
int schedselect()
{
//function to display what algorithms can be selected. User input
// obtained based on these options and user filtered based on switch
// cases to relevant function path
char selection;
// print users options and take their input for switch
printf("%s",buffer);
printf("\n\n\nPlease select the Scheduling Algorithm you would like to use\n\n");
printf(" 1. First Come First Served (FCFS)\n 2. Shortest Job First (SJF)\n 3. Round Robin (RR)\n 4. Quit\n\nSelection:\n");
scanf("%c",&selection);
// direct user to specific algorithm function path
switch(selection)
{
case '1':
//printf("\nYou have selected First Come First Served (FCFS)\n");
schedintro(schedtoken=1);
break;
case '2':
//printf("\nYou have selected Shortest Job First (SJF)\n");
schedintro(schedtoken=2);
break;
case '3':
//printf("\nYou have selected Round Robin (RR)\n");
schedintro(schedtoken=3);
break;
case '4':
printf("\nThank you for using this tool!");
break;
default:
printf("\nERROR!: Incorrect selection - Returning to Menu\n");
schedselect();
}
//printf("%d", schedoption);
return schedtoken;
}
int main()
{
strcpy(filename, "headers/introheader.txt");
getfile(filename);
schedselect();
return 0;
}
答案 0 :(得分：1)
在 fcfs（）中，您关闭同一文件两次
fclose(fp); //compare values in arr time to find earliest arrival time. Basically loops through dataset values and sorts them into the arrival order
和
fclose（fp）;
//打开新文件以打印输出
删除第二个 fclose
在没有第二个 fclose 的情况下，-emsetset_的 valgrind 不会发出任何信号：
valgrind ./a.out
==22836== Memcheck, a memory error detector
==22836== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==22836== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==22836== Command: ./a.out
==22836==
(null)
Please select the Scheduling Algorithm you would like to use
1. First Come First Served (FCFS)
2. Shortest Job First (SJF)
3. Round Robin (RR)
4. Quit
Selection:
1
(null)
Please select the dataset you would like to use
1. Dataset1
2. Dataset2
3. Dataset3
4. Quit
Selection:
3
You have selected Dataset3
PID AT BT WT ST TAT CT
3 0 25 0 0 25 25
1 1 5 24 25 29 30
2 2 20 28 30 48 50
0 3 4 47 50 51 54
4 6 14 48 54 62 68
5 8 6 60 68 66 74
Average Waiting Time:34.500000
Average Turn Around Time:46.833332
The results for the dataset simulated are stored in: datasets/output.txt==22836==
==22836== HEAP SUMMARY:
==22836== in use at exit: 0 bytes in 0 blocks
==22836== total heap usage: 4 allocs, 4 frees, 2,272 bytes allocated
==22836==
==22836== All heap blocks were freed -- no leaks are possible
==22836==
==22836== For counts of detected and suppressed errors, rerun with: -v
==22836== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 6)
答案 1 :(得分：1)
除了bruno指出的双重免费问题外，您的代码还存在编写错误。
char c1,c2,c3,fcfsselection;
...
fscanf(fp,"%s%s%s",&c1,&c2,&c3); // out-of-bounds write.
这里是live test of your code，它报告此错误。