c - 访问指针元素时出现分段错误

Question

#include <stdio.h>
#include <stdlib.h>
#include "frac_heap.h"

#define ARRAYSIZE 10
#define ENDOFARRAY 999

fraction heap[ARRAYSIZE] = {0};
block freeBlocks[ARRAYSIZE] = {0};
int startingBlock = 0;
int nextFree = 0;
fraction* fracPointers[][ARRAYSIZE] = {0};
block* blockPointers[][ARRAYSIZE] = {0};

void init_Heap(){
    int x;
    for(x = 0; x < ARRAYSIZE; x ++){    
        block *currBlock = &freeBlocks[x];
        currBlock->isFree = 1;  
        fraction *fractionPointer = &heap[x];
        if(x<ARRAYSIZE - 1){
            fractionPointer->denominator = x+1;
        }
        else if(x == ARRAYSIZE - 1){
            fractionPointer->denominator = ENDOFARRAY;
        }
    }
}

void dump_heap(){
    int x;
    for(x = 0; x < ARRAYSIZE; x ++){
        fraction* tempFrac = &heap[x];
        printf("%d\t%d\t%d\n",tempFrac->sign, tempFrac->numerator, tempFrac->denominator);
    }   
}

fraction* new_frac(){

    fraction* testFraction = &heap[0];
    if(testFraction->numerator == 0 && testFraction ->denominator==0){
        printf("Before return");        
        return testFraction;
    }
}

int main(){

    init_Heap();
    dump_heap();
    fraction *p1;
    p1 = new_frac();
    p1->sign = -1;
    p1->numerator  = 2;
    p1->denominator = 3;
    dump_heap();
   }

尝试调用 new_frac() 时出现分段错误。此时我只是测试代码，我意识到 testfraction 不会总是 = &heap[0];。但是，我认为我能够访问我用'->'指向的部分结构？

在对其进行更多编辑之后，它似乎只有在达到 testFraction->denominator 时才会出现段错误。如果我只检查分母，它仍然会出现段错误，但它只适用于分子。

Answer 1

问题是并非所有通过的代码路径new_frac()实际上都返回一个值。然后，您继续通过这个可能未初始化的指针进行分配：

p1 = new_frac();
p1->sign = -1;
p1->numerator  = 2;
p1->denominator = 3;