c - 尝试使用联合来索引结构中的数据

Question

我正在尝试从以a：b：c：d：e：f格式存储数据的文件中检索数据，我想使用union来索引struct中的每个字段。也就是说，我应该定义union和struct如下，但是当我尝试使用联合/结构时，我遇到了一堆警告，当然还有分段错误错误。

#define _XOPEN_SOURCE
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define FIELDS 6
typedef union{
  char a[FIELDS];
  struct {
    char* a;
    char* b;
    char* c;
    char* d;
    char* e;
    char* f;
  } s;
} Elements;
int main(int argc, char const *argv[]) {
  if (argc != 2) {
    fprintf(stderr, "Usage: %s datan", argv[0]);
    exit(EXIT_FAILURE);
  }
  const int COLONS = 5;
  const int MAXFIELDS = 5000;
  char *buffer = 0;
  char *token = 0;
  size_t len = 0;
  size_t field_length = 0;
  ssize_t nread;
  Elements* totalElements = malloc(MAXFIELDS);
  int total_elements = 0;
  FILE *fp;
  fp = fopen (argv[1], "r");
  if (fp == NULL) {
    perror("fopen");
    exit(EXIT_FAILURE);
  }
  while ((nread = getline(&buffer, &len, fp)) != 1) {
    token = strtok(buffer, ":");
    field_length = snprintf( NULL, 0, "%s", token );
    totalElements[total_elements].a[0] = malloc( field_length );
    strcpy (totalElements[total_elements].a[0], token);
    for (int i = 1; i < COLONS - 1; i++){
      field_length = snprintf( NULL, 0, "%s", token );
      totalElements[total_elements].a[i] = malloc( field_length );
      strcpy (totalElements[total_elements].a[i], token);
      token = strtok(NULL, ":");
    }
    field_length = snprintf( NULL, 0, "%s", token );
    totalElements[total_elements].a[COLONS - 1] = malloc( field_length );
    strcpy (totalElements[total_elements].a[COLONS - 1], token);
    token = strtok(NULL, "n");
    field_length = snprintf( NULL, 0, "%s", token );
    totalElements[total_elements].a[COLONS] = malloc( field_length );
    strcpy (totalElements[total_elements].a[COLONS], token);
    total_elements++;
  }
  fclose (fp);
  free (buffer);
  free (totalElements);
  exit(EXIT_SUCCESS);
  return 0;
}

编译器 gcc 显示的警告：

ex.c:51:40: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
     totalElements[total_elements].a[0] = malloc( field_length );
                                        ^ ex.c:52:13: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
     strcpy (totalElements[total_elements].a[0], token);
             ^~~~~~~~~~~~~ In file included from ex.c:6:0: /usr/include/string.h:121:14: note: expected ‘char * restrict’ but argument is of type ‘char’  extern char *strcpy (char *__restrict
__dest, const char *__restrict __src)
              ^~~~~~ ex.c:57:42: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
       totalElements[total_elements].a[i] = malloc( field_length );
                                          ^ ex.c:58:15: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
       strcpy (totalElements[total_elements].a[i], token);
               ^~~~~~~~~~~~~ In file included from ex.c:6:0: /usr/include/string.h:121:14: note: expected ‘char * restrict’ but argument is of type ‘char’  extern char *strcpy (char *__restrict
__dest, const char *__restrict __src)
              ^~~~~~ ex.c:65:49: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
     totalElements[total_elements].a[COLONS - 1] = malloc( field_length );
                                                 ^ ex.c:66:13: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
     strcpy (totalElements[total_elements].a[COLONS - 1], token);
             ^~~~~~~~~~~~~ In file included from ex.c:6:0: /usr/include/string.h:121:14: note: expected ‘char * restrict’ but argument is of type ‘char’  extern char *strcpy (char *__restrict
__dest, const char *__restrict __src)
              ^~~~~~ ex.c:71:45: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
     totalElements[total_elements].a[COLONS] = malloc( field_length );
                                             ^ ex.c:72:13: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
     strcpy (totalElements[total_elements].a[COLONS], token);
             ^~~~~~~~~~~~~ In file included from ex.c:6:0: /usr/include/string.h:121:14: note: expected ‘char * restrict’ but argument is of type ‘char’  extern char *strcpy (char *__restrict
__dest, const char *__restrict __src)
              ^~~~~~

Answer 1

联合中的char a[FIELDS]字段应该是char * a[FIELDS]的，因为结构是char *的，char a[]不是char *数组，而是char数组。