Valgrind大小為8的無效寫入

Question

我正在嘗試使用C結構，但我想出了一個invalid write of size 8然后從valgrind invalid read of size 8消息。

我的代碼僅循環遍歷參數（如果argc > 1 ），並且對於每個文件名，它將掃描string和unsigned int指示名稱和年齡（結構播放器）。

這是我到目前為止所擁有的所有代碼：

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

struct player {
  char name[20];
  unsigned int age;
};

struct player *player_new_from_stream(FILE * stream){
  struct player *new_player = (struct player*) malloc(sizeof(struct player));
  char *p_name = malloc(20);
  char *p_age = malloc(20);

  if (stream != stdin){
    if (fgets(p_name, 20, stream) != NULL){
      char *p = strrchr(p_name, '\n');
      if (p)
        *p = '\0';
      strcpy(new_player->name, p_name);
    }
    if (fgets(p_age, 20, stream) != NULL)
      new_player->age = atoi(p_age);
  }
  else {
    printf("enter name and age for a player\n");
    gets(p_name);
    gets(p_age);
    strcpy(new_player->name, p_name);
    new_player->age = atoi(p_age);
  }

  free(p_name);
  free(p_age);
  return new_player;
}

void player_inspect(struct player plyr, char* prefix){
  printf("[%s] name: %s\n", prefix, plyr.name);
  printf("[%s] age : %d\n", prefix, plyr.age);
}

int main(int argc, char* argv[]){
  FILE * stream;
  char* argument;
  // below: trying to allocate (argc - 1) pointers
  // valgrind's --show-origins=yes points here for both errors
  struct player **players = malloc(sizeof(int) * (argc - 1)); 
  int i = 1;
  for (; i < argc; i++){
    argument = argv[i];
    if (strcmp("-", argument) != 0){
      if ((stream = fopen(argument, "r")) == NULL) perror("Error opening file");
      else {
        // the next line emits Invalid write of size 8 in valgrind
        players[i-1] = player_new_from_stream(stream);
        fclose(stream);
      }
    } else {
      players[i-1] = player_new_from_stream(stdin);
    }
  }

  i = 0;
  char buffer[15];
  for (; i < argc - 1; i++){
    sprintf(buffer, "%d", i);
    // the next line emits Invalid read of size 8
    player_inspect(*(players[i]), buffer);
    free(players[i]);
  }

  free(players);
  return 0;
}

怎么了 我想從player_new_from_stream返回一個指向struct player的指針，並將該指針打包到main()數組players 。

Answer 1

這是錯誤的：

struct player **players = malloc(sizeof(int) * (argc - 1));

使用此代替：

struct player **players = malloc(sizeof(*players) * (argc - 1));

請注意，在您的系統上， sizeof(int) == 4而sizeof(struct player *) == 8 。

Answer 2

如果要使用數組，則需要進行兩次分配：

struct player **players = malloc(sizeof(struct player*) * (argc - 1));
for (int i=0; i<argc-1;i++)
   player[i] = malloc(sizeof(struct player));

Answer 3

我在valgrind下使用有效的輸入文件（播放器文件）運行了該文件，並使用gcc -g進行了編譯，但是它沒有給出任何這些無效的讀/寫消息。

它也適用於使用stdin。

但是，當我使用不存在的文件運行它時，它在讀取時出現錯誤

  i = 0;
  char buffer[15];
  for (; i < argc - 1; i++){
    sprintf(buffer, "%d", i);
    player_inspect(*(players[i]), buffer); // <<HERE
    free(players[i]);
  }

由於players [i]指針為NULL，因為如果fopen調用失敗，則未設置該數組索引處的指針。