在 C 中为我的进程调度模拟器程序逐行读取文件时出现分段错误（核心转储）错误

Question

I have a program that takes information about processes from a text file, and then uses the desired CPU scheduling algorithm to schedule the process and print them accordingly.

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<sys/time.h>
#include<time.h>

//Structure to store the information about a process
typedef struct{

    int pid;
    int arrival;
    int burst;

}Processes;

//Array of structure
typedef struct
{
    Processes *array;
    size_t used;
    size_t size;
} Array;

enum ALGORITHM_TYPE{FCFS, RR, SRTF};                        //enum for creating the algorithm types
int procNum = 0;                                            //Variable to keep track of number of processes
Array proc, fin;


//Function to determine the number of processes
void procNumFunction(char *fileName){

    FILE *fp;                                               //File pointer
    char *buffer, c;

    fp = fopen(fileName, "r");
    if(fp == NULL)
        exit(1);

    // Extract characters from file and store in character c
    for (c = getc(fp); c != EOF; c = getc(fp))
        if (c == '\n') // Increment count if this character is newline
            procNum++;

    printf("\nTotal %d tasks are read from \"%s\"\n\n", procNum, fileName);

}

//function to dynamically fill the array
void initArray(Array *a, size_t initialSize)
{
    // Allocate initial space
    a->array = (Processes *)calloc(initialSize, sizeof(Processes));

    a->used = 0;                                            // no elements used
    a->size = initialSize;                                  // available nr of elements
}

// Add element to array
void insertArray(Array *a, Processes element)
{

    if (a->used == a->size)
    {
        a->size *= 2;
        a->array = (Processes *)realloc(a->array, a->size * sizeof(Processes));
    }

    a->array[a->used].pid=element.pid;
    a->array[a->used].arrival=element.arrival;
    a->array[a->used].burst=element.burst;
    a->used++;

}

//Functino to free array
void freeArray(Array *a)
{

    free(a->array);
    a->array = NULL;
    a->used = 0;
    a->size = 0;

}

//Function to read from the file
void readFile(char *fileName){

    FILE *fp = NULL;                                               //File pointer
    char *buffer = NULL, *pid = NULL, *arr = NULL, *bur = NULL,*p = NULL;
    Processes temp;
    int count = 0;

    fp = fopen(fileName, "r");
    if(fp == NULL)
        exit(1);

    //Loop to read the file line by line
    while(fgets(buffer, sizeof(buffer), fp)){

/*        copyToken(pid, buffer, sizeof(pid), "\t");
        copyToken(arr, buffer, sizeof(arr), "\t");
        copyToken(bur, buffer, sizeof(bur), "\n");*/

        while (*p) {

            if ( isdigit(*p) || ( (*p=='-'||*p=='+') && isdigit(*(p+1)) )) {

                // Found a number
                long val = strtol(p, &p, 10); // Read number
                if(count == 0){

                    temp.pid = val;
                    count++;

                }
                else if(count == 1){

                    temp.arrival = val;
                    count++;

                }
                else if(count == 3){

                    temp.burst = val;
                    count++;

                }
            } else {

                p++;
            }
        }

        //Insert element into array
        insertArray(&proc, temp);
        count = 0;

    }
    fclose(fp);

}

/*void copyToken(char * dest, char *source, int len, char const *delim){

    char *token = strtok(source, delim);
    if(token != NULL){

        dest[0] = '\0';
        strncat(dest, token, len-1);

    }

}*/

void fcfs(char *fileName){

    int finCount = 0, sysTime = 0;

    //Calling this function to determine the number of processes
    procNumFunction(fileName);

    //Initializing the array
    initArray(&proc, procNum);
    initArray(&fin, procNum);

    //Reading the file
    readFile(fileName);

    while(finCount <= procNum){

        printf("<system time\t%d> process %d is running\n", sysTime, proc.array[finCount].pid);
        sysTime++;
        if(proc.array[finCount].burst != 0)
            proc.array[finCount].burst--;
        else{

            printf("<system time\t%d> process %d is finished...\n", sysTime, proc.array[finCount].pid);
            finCount++;

        }

    }

    if(finCount > procNum){

        printf("<system time\t%d> All processes finished\n", sysTime);
        printf("==================================================================================\n");

    }

}

void srtf(char * fileName){



}

//The main function of the program
int main(int argc, char *argv[]){

    //Conditions to check if the arguments have been given correctly or not
    if (argc < 2)
        printf("Error. File name missing !!!");
    else if(argc == 2)
        printf("Error. Scheduling type missing !!!");
    else{

        if(!(strcmp(argv[2],"FCFS"))){

            printf("Scheduling algorithm: %s", argv[2]);
            fcfs(argv[1]);                                  //call FCFS

        }
        else if(!(strcmp(argv[2], "RR"))){

            printf("Scheduling algorithm: %s\n", argv[2]);
            if(argc != 4)
                printf("Error. Time quantum not given !!!");
            else{

                //check if valid input

            }

        }
        else if(!(strcmp(argv[2], "SRTF"))){

            printf("Scheduling algorithm: %s", argv[2]);
            srtf(argv[1]);                                  //call SRTF

        }

    }

}

My code is not complete at this point, but it compiles and runs. I just wanted to run the program and see if my program is working correctly for at least the FCFS algorithm.

I tested the program using this file named input1.txt

1 0 10
2 0 9
3 3 5
4 7 4
5 10 6
6 10 7

Here, the first numbe is the PID for the process, the second number is the Arrival time for the process and the third number is the Burst time for the process. In total, there are 6 processes.

My problem here is that when I run the program, it manages to run with the following output:

$ ./a.out input1.txt FCFS
Scheduling algorithm: FCFS
Total 5 tasks are read from "input1.txt"

Segmentation fault (core dumped)

What I don't understand here is that my am I getting a segmentation fault, and after running through the eclipse debugger, the program stops at the line while(fgets(buffer, sizeof(buffer), fp)){ in the readFile function. Can anyone help me as to what I am doing wrong because I think my implementation for reading a file line by line is correct?

Thanks in advance.

Answer 1

Your buffer is a pointer to nowhere (no space for the string allocated, ever!). It's size is the size of a pointer (4 or 8 bytes), not space for placing anything. Make your buffer an array of eg 100 bytes (temporary storage!), ie char buffer[100] .

Answer 2

1. Open the file in procNumFunction() but didn't fclose() , then in readFile() you try open it again.

2. procNum=0; and initArray(&proc, procNum); makes calloc(0, sizeof(Processes))
   i'm not sure what will happen on calling calloc(0), but malloc(0) is wrong here. (somewhere use malloc(0) but here is not good)

void *malloc(size_t size);

malloc() allocates size bytes and returns a pointer to the allocated memory. The memory is not cleared. If size is 0 , then malloc() returns either NULL, or a unique pointer value that can later be successfully passed to free().

3. after initArray , a->used is 0, a->size is 0, then insertArray()

a->size *= 2;
a->array = (Processes *)realloc(a->array, a->size * sizeof(Processes));

make a realloc(p, 0) calling, i think it's dangerous.

Answer 3

in function: readFile() , the pointer p is initialized to NULL

Then this statement is executed:

while (*p) {

And since p contains NULL, the program will crash with a seg fault event.