c - 结构体数组内存 realloc stderr

Question

当我将元素放入其中时，我试图在空间不足时重新分配结构数组，但我不断收到重新分配的标准错误。 struct 数组最终将包含 235,000 个元素。当我将初始启动大小设置为 100,000 时，我在尝试重新分配时收到了 stderr。如果我将初始启动大小设置为 300,000，它不会给出错误，因为它永远不会到达 realloc 语句。

#define _XOPEN_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include <string.h>

#define BUFFERLEN 200
#define START_SIZE 100000
#define GROW 1000
#define TRUE 1
#define FALSE 0

typedef struct{
    char *forw;
    char *back;
} word;

typedef struct{
    char *entry;
} single_words;


FILE *words;
/*-------------Function Prototypes------------*/
void reverse(char* string, char* revstr, int len);
int search_struct(char* find, word* words, int length);
int compare(const void* eventa, const void* eventb);
int length(char* string);


int main(void)
{
    char *buffer;
    int letter_index[26];
    char alpha[] = "abcdefghijklmnopqrstuvwxyz";
    int i=0, found = FALSE, strlen=0, letter=0;
    word *word_storage;
    single_words *output_storage;
    int num_words = 0, size = 0;
    int num_output = 0, output_size = 0;

    /*buffer for the input strings of the words in the input file*/
    buffer = (char*) malloc (sizeof(char)*BUFFERLEN);
        if(!buffer){
            fprintf(stderr, "Error in buffer string mem alloc\n");
            exit(1);
        }   

    /*Initializing the array of structs to store the forward and reverse of each word*/
    word_storage = (word*) malloc (sizeof(word)*START_SIZE);
        if(!word_storage){
            fprintf(stderr, "Error in word_storage string mem alloc\n");
            exit(1);
        }
        size = START_SIZE;

    /*Initializing the array of structs for the output*/
    output_storage = (single_words*) malloc (sizeof(single_words)*START_SIZE);
        if(!output_storage){
            fprintf(stderr, "Error in output_storage mem alloc\n");
            exit(1);
        }
        output_size = START_SIZE;   

    /*Set the letter index 0(which is a) to the first character*/
    letter_index[0] = 0;

    words = fopen("words", "r");

    /*Read the words(forward and reverse) in from stdin into the word_storage*/
    while(fgets(buffer, BUFFERLEN, words) != NULL){
        buffer = strtok(buffer, "\n");
        strlen = length(buffer);
        if (num_words < size){
            /*Allocate memory for the forward and reverse strings*/
            word_storage[num_words].forw = (char *) malloc (sizeof(char) * strlen);
                if(!word_storage[num_words].forw){
                    free(word_storage[num_words].forw);
                    fprintf(stderr, "word_storage forward string malloc was unsuccessful");
                    exit(1);
                }
            word_storage[num_words].back = (char *) malloc (sizeof(char) * strlen);
                if(!word_storage[num_words].back){
                    free(word_storage[num_words].back);
                    fprintf(stderr, "word_storage forward string malloc was unsuccessful");
                    exit(1);;
                }               

            /*Store the forward and reverse in the strings*/
            strncpy(word_storage[num_words].forw, buffer, strlen);
            reverse(word_storage[num_words].forw, word_storage[num_words].back, strlen);
            printf("%d: %s %s\n", num_words, word_storage[num_words].forw, word_storage[num_words].back);

            /*Increment the letter if it changes*/
            if(word_storage[num_words].forw[0] != alpha[letter]){
                letter++;
                letter_index[letter] = num_words + 1;
            }
            num_words++;
        }
        else{
            /*Increase the size of word_storage*/
            word_storage = (word*) realloc (word_storage, sizeof(word) * size * GROW);
                if(!word_storage){
                    free(word_storage);
                    fprintf(stderr, "Error in word_storage realloc string mem realloc\n");
                    exit(1);
                }
            size = size * GROW;
        }       
    }


    return 0;
}

此处发生重新分配错误:

word_storage = (word*) realloc (word_storage, sizeof(word) * size * GROW);
    if(!word_storage){
      free(word_storage);
      fprintf(stderr, "Error in word_storage realloc string mem realloc\n");
      exit(1);
     }
     size = size * GROW;

Answer 1

因此，您最初将 size 设置为 START_SIZE，即 100,000。然后，当您用完它时，您尝试分配 sizeof(word) * size * GROW 字节。 sizeof(word) 大概是 16 个字节；我们知道 size 是 100000，GROW 是 1000。因此，这足以容纳 100,000,000 个条目，您说您将使用其中的 235,000 个条目。看来分配有点慷慨了。

100,000,000 个条目的总空间为 1,600,000,000 字节。这似乎很多，尽管现在许多台式机都可以处理这个问题。但 realloc 失败似乎并不太令人惊讶。

也许你应该让 GROW 更合理，比如 2。

顺便说一句，一旦确定 word_storage 为 NULL，调用 free(word_storage) 就没有意义了。它没有任何害处，因为 free(NULL) 是一个无操作，但出于同样的原因它也没有任何好处。