c - 通过引用传递时动态调整结构数组大小

Question

在以下第一轮之后我不明白导致段错误的原因:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct query_param {
  char *key;
  char *val;
};

void extract_params(struct query_param **query_params, char *query_string,
                    size_t *query_params_len) {
  char *token, *key;

  while (query_string != NULL) {
    token = strsep(&query_string, "&");
    key = strsep(&token, "=");

    *query_params = realloc(*query_params, (*query_params_len + 1) *
                                               sizeof(struct query_param));


    query_params[*query_params_len]->key = malloc(strlen(key));
    query_params[*query_params_len]->val = malloc(strlen(token));

    memcpy(query_params[*query_params_len]->key, key, strlen(key));
    memcpy(query_params[*query_params_len]->val, token, strlen(token));

    (*query_params_len)++;
  }
}

int main(int argc, char **argv) {
  char *query_string = "foo=bar&baz=boo&zip=zap";
  size_t query_params_len = 0;
  struct query_param *query_params = NULL;
  extract_params(&query_params, query_string, &query_params_len);
  return 0;
}

将第一个键值对添加到结构中工作正常，但第二个 malloc 导致问题。

valgrind 信息:

==15319== Memcheck, a memory error detector
==15319== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==15319== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==15319== Command: ./a.out
==15319== 
==15319== 
==15319== Process terminating with default action of signal 11 (SIGSEGV)
==15319==  Bad permissions for mapped region at address 0x4008DF
==15319==    at 0x4EC1A0B: strsep (in /lib64/libc-2.23.so)
==15319==    by 0x4006C0: extract_params (foo.c:15)
==15319==    by 0x400848: main (foo.c:36)
==15319== 
==15319== HEAP SUMMARY:
==15319==     in use at exit: 0 bytes in 0 blocks
==15319==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==15319== 
==15319== All heap blocks were freed -- no leaks are possible
==15319== 
==15319== For counts of detected and suppressed errors, rerun with: -v
==15319== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

运行 valgrind 后，仍然没有解决这个问题。特别是堆摘要对我来说没有任何意义。运行malloc 3次后怎么会分配0个字节？

干杯!

Answer 1

 query_params[*query_params_len]->blah

query_params 不是指针数组，也不是指针数组的第一个元素的指针。它是一个指向结构数组第一个元素的指针。你想要这个

 (*query_params)[*query_params_len].blah