我正在尝试将文件读入数组并不断收到此错误

Question

help me please. I'm trying to read a file into an array and return the max amount of numbers in the file. I keep getting a segmentation fault error and I know its probably because of how I'm handling the Array but I can find the exact issue, The issue is in the function ReadFileInotArray. After the function is over I get the error shown below.

#include <stdlib.h> 
#include <stdio.h> 
#include <string.h>
#include <time.h>
void PrintArray(int ArrayToPrint[], int SizeAP)
{
    int i;
    printf("{");
    for (i=0; i< SizeAP; i++)
        printf("%d,", ArrayToPrint[i]);
    printf("\b}\n");
}

void swap(int *SwapA, int *SwapB)
{
    int temp = *SwapA;
    *SwapA = *SwapB;
    *SwapB = temp;
}

int partition (int A[], int low, int high) 
{ 
    int i, j = 0;
    #if QSM
    int middle = (high+low)/2;
    swap(&A[middle], &A[high]);
    #elif QSRND
    int random = (rand() % (high-low+1)) + low;
    swap(&A[random], &A[high]);
    #endif
    int pivot = A[high];
    i= (low - 1); 
    for (j = low; j < high; j++) 
    { 
        if (A[j] < pivot) 
        { 
            i++; 
            swap(&A[i], &A[j]);
        } 
    } 
    swap(&A[i+ 1], &A[high]);
    return (i+ 1);
}

void QuickSort(int A[], int low, int high) 
{ 
    if (low < high) 
    {
       int ndx= partition(A, low, high);
       QuickSort(A, low, ndx-1); 
       QuickSort(A, ndx+ 1, high); 
    } 
}

void ReadFileIntoArray(int argc, char *argv[], int A[],int size)
{
    char line[200];
    int j=0;
    if(argv[1]==NULL) 
    {   
        printf("File must be provided on command line...exiting\n");
        exit(0);
    }
    
    FILE *fp = fopen(argv[1],"r");
    
    if(fp==NULL) 
    {
        printf("Exiting: no such file in directory\n");
        exit(0);
    }
    while(fgets(line,200,fp)!=NULL) 
    {
        size++;
    }
    fseek(fp,0,0); 
    A=malloc(sizeof(int)*size);
    while(j<size && fgets(line,200,fp)!=NULL ) 
    {
    
        A[j]=atoi(line);
        printf("%d\n",A[j]);
        j++;
    }
    printf("%d",size);
    PrintArray(A,size);

}

int main(int argc ,char *argv[]) 
{ 
    clock_t start,end;
    int i,control,count=0,size;
    int *array;
    
    if(argv[2]==NULL)
    { 
        printf("Number of runs not specified on the command line...defaluting to 10");
        control=10;
    }
    else 
        control=atoi(argv[2]);
    for(i=1; i<=control; i++)
    {
        ReadFileIntoArray(argc,argv,array,size);
        #ifdef PRINTARRAY
        PrintArray(array, size);
        #endif
        printf("ok");
        start = clock();
        QuickSort(array, 0, size-1);
        end = clock();
        printf("\nRun %d complete: %ld tics",i ,end-start);
        count+=end-start;
    
        #ifdef PRINTARRAY
        PrintArray(array,size);
        #endif
    
        free(array);
    }
    printf("\nThe average run time for %s runs is %d\n",argv[2],count/i);
    printf("\nProcessed %d records\n",size);
    return 0; 
} 

Here is the output I get when running in the VM.

student@maverick:/media/sf_VM_folder/CSE_3318_code@ gcc Code3_1001472179.c 
student@maverick:/media/sf_VM_folder/CSE_3318_code$ ./a.out TestFile.txt 5
472179
93424
313939
263358
154966
93659
221593
284590
439245
154572
10{472179,93424,313939,263358,154966,93659,221593,284590,439245,154572}
ok
munmap_chunk(): invalid pointer
Aborted (core dumped)

Answer 1

You haven't pasted complete code but I'm assuming here's what's happening. You've just passed in array from main directly. Your modifications to A in ReadFileIntoArray() won't be reflected in main() and since you haven't even initialized array , accessing it in main() is Undefined Bevahoiour and probably a crash. You need to pass in &array and accept an int** A in ReadFileIntoArray()

PS There's bug with how you use size too since the changes made to size in ReadFileIntoArray() won't be reflected back in main() , You need to pass in &size and accept int* size in ReadFileIntoArray() .

EDIT: You're exactly doing what I'd assumed. When you call QuickSort(array, 0, size-1); , array doesn't have any values and points to some indeterminate value (or possibly NULL ).

I'll share a small example to explain what's wrong.

void readIntoArray(int array[], int size) {
    printf("%s: Initial values %p - %d\n", __FUNCTION__, array, size);
    //code to read the vale of size from file
    size = 5;
    array = malloc(sizeof(int) * size);
    printf("%s: End values %p - %d\n", __FUNCTION__, array, size);
}

int main() {
    int * array;
    int size;
    printf("%s: Initial values %p - %d\n", __FUNCTION__, array, size);
    readIntoArray(array, size);
    printf("%s: End values %p - %d\n", __FUNCTION__, array, size);
}

This, on some compiler , could yield output like:

main: Initial values (nil) - 32766
readIntoArray: Initial values (nil) - 32766
readIntoArray: End values 0x2435020 - 5
main: End values (nil) - 32766

Note what's happening here. Even though you changed array inside readIntoArray() to point to some malloc 'd memory, that doesn't reflect back in the main() . Same is the case with size . This is a very basic concept in C wherein arguments are passed to functions by value and are copied. To have the changes done in readIntoArray , you need to pass them by reference by passing in their addresses using the & operator, something like this :

void readIntoArray(int **array, int* size) {
    printf("%s: Initial values %p - %d\n", __FUNCTION__, *array, *size);
    //code to read the vale of size from file
    *size = 5;
    *array = malloc(sizeof(int) * *size);
    printf("%s: End values %p - %d\n", __FUNCTION__, *array, *size);
}

int main() {
    int * array;
    int size;
    printf("%s: Initial values %p - %d\n", __FUNCTION__, array, size);
    readIntoArray(&array, &size);
    printf("%s: End values %p - %d\n", __FUNCTION__, array, size);
}

which yields the output:

main: Initial values (nil) - 32766
readIntoArray: Initial values (nil) - 32766
readIntoArray: End values 0x1217020 - 5
main: End values 0x1217020 - 5

PS These are just examples and when dealing with pointers, it's always best to check for them being NULL before dereferencing them like *array , *size .