c - 将 bsearch 与字符串数组一起使用时出现问题

Question

我在尝试对 C 中的字符串数组使用 c 内置 bsearch 时遇到一些令人困惑的行为。这是代码。我知道您可以使用内置的 strcmp 来搜索字符串数组，但我包含了 myStrCmp 用于调试目的，因为我不知道为什么它不起作用。

const char *stateNames[] = {"Alabama", "Alaska", "Arizona", "Arkansas", "California", "Colorado", "Connecticut", "Delaware", "Florida", "Georgia", "Hawaii", "Idaho", "Illinois", "Indiana", "Iowa", "Kansas", "Kentucky", "Louisiana", "Maine", "Maryland", "Massachusetts", "Michigan", "Minnesota", "Mississippi", "Missouri", "Montana", "Nebraska", "Nevada", "New Hampshire", "New Jersey", "New Mexico", "New York", "North Carolina", "North Dakota", "Ohio", "Oklahoma", "Oregon", "Pennsylvania", "Rhode Island", "South Carolina", "South Dakota", "Tennessee", "Texas", "Utah", "Vermont", "Virginia", "Washington", "Washington DC", "West Virginia", "Wisconsin", "Wyoming"};

int myStrCmp(const void *s1, const void *s2) {
  printf("myStrCmp: s1(%p): %s, s2(%p): %s\n", s1, (char *)s1, s2, (char *)s2);
  return strcmp(s1, s2);
}

int determineState(char *state) {
  printf("state: %s\n", state);
  for(int i = 0; i < 51; i++) 
    printf("stateNames[%i](%p): %s\n", i, &(stateNames[i]), stateNames[i]);

  char *found = (char *) bsearch(state, stateNames, 51, sizeof(char *), myStrCmp );

  if(found == NULL)
    return -1;

  return 0;
}

这是调用此函数以查找阿拉巴马州时的一些输出。

stateNames[0](0x618440): Alabama
stateNames[1](0x618448): Alaska
stateNames[2](0x618450): Arizona
...
stateNames[24](0x618500): Missouri
stateNames[25](0x618508): Montana
stateNames[26](0x618510): Nebraska
stateNames[27](0x618518): Nevada
stateNames[28](0x618520): New Hampshire
stateNames[29](0x618528): New Jersey
stateNames[30](0x618530): New Mexico
stateNames[31](0x618538): New York
stateNames[32](0x618540): North Carolina
stateNames[33](0x618548): North Dakota
stateNames[34](0x618550): Ohio
stateNames[35](0x618558): Oklahoma
stateNames[36](0x618560): Oregon
stateNames[37](0x618568): Pennsylvania
stateNames[38](0x618570): Rhode Island
stateNames[39](0x618578): South Carolina
stateNames[40](0x618580): South Dakota
stateNames[41](0x618588): Tennessee
stateNames[42](0x618590): Texas
stateNames[43](0x618598): Utah
stateNames[44](0x6185a0): Vermont
stateNames[45](0x6185a8): Virginia
stateNames[46](0x6185b0): Washington
stateNames[47](0x6185b8): Washington DC
stateNames[48](0x6185c0): West Virginia
stateNames[49](0x6185c8): Wisconsin
stateNames[50](0x6185d0): Wyoming
myStrCmp: s1(0x415430): Alabama, s2(0x618508): 
                                               UA
myStrCmp: s1(0x415430): Alabama, s2(0x618570): A
myStrCmp: s1(0x415430): Alabama, s2(0x618540): PUA
myStrCmp: s1(0x415430): Alabama, s2(0x618528): 1UA
myStrCmp: s1(0x415430): Alabama, s2(0x618538): GUA
myStrCmp: s1(0x415430): Alabama, s2(0x618530): <UA

如您所见，bsearch 在其搜索过程中访问的位置应该具有有效字符串(正如在调用 bsearch 之前刚刚检查的那样)，但是如果您尝试在该位置打印 char *，则输出是垃圾。谁能看到我的错误？顺便说一句，当我调用 bsearch 并将最终参数设置为:

(int(*)(const void*, const void*))strcmp

谢谢!

Answer 1

由于您使用的是 const char * 数组，bsearch() 会将指向这些元素的指针传递给比较函数。换句话说，它将在第二个参数中接收 const char * const *。

int myStrCmp(const void *s1, const void *s2) {
  const char *key = s1;
  const char * const *arg = s2;
  printf("myStrCmp: s1(%p): %s, s2(%p): %s\n", s1, key, s2, *arg);
  return strcmp(key, *arg);
}