Question

我试图在空间用完时重新分配一个结构数组，因为我正在将元素放入其中，但我一直收到一个realloc stderr。 struct数组最终将包含235,000个元素。当我将初始起始大小设置为100,000时，我在尝试重新分配时收到stderr。如果我将初始起始大小设置为300,000，则不会给出错误，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realloc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，当您使用它时，您尝试分配sizeof(word) * size * GROW个字节。 sizeof(word)大概是16个字节;我们知道size是100000，而GROW是1000.所以这足以容纳100,000,000个条目，其中你说你将使用235,000个。这看起来似乎有点慷慨。

100,000,000个条目的总空间为1,600,000,000个字节。这似乎很多，虽然现在很多台式机都可以处理。但realloc失败似乎太令人惊讶。

也许你应该让GROW更合理，比如2。

顺便说一下，一旦你确定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，但它也没有任何好处。

Answer 2

您将大小乘以1000这是太多了（高指数增长1 - > 1000 - > 1000 000 - > 1000 000 000 ......），而您没有显示errno 。我建议改为

 size_t newsize = 3*size/2 + 1000;
 word_storage = realloc(word_storage, sizeof(word)*newsize);
 if (!word_storage) {
     fprintf(stderr, "Cannot grow storage to %ld size, %s\n",
                     (long) newsize, strerror(errno));
     exit (EXIT_FAILURE);
 }
 else size = newsize;

然后，如果从初始大小1000开始，您将获得更合理的进展1000 - ＆gt; 2500 - ＆gt; 4750 - ＆gt; 8125 - ＆gt; 13187 - ＆gt; 20780 ......更重要的是，你花费了最多50％的无用记忆，而不是近1000的因素！

结构数组内存realloc stderr

2 个答案: