问题描述
我对 C 完全陌生，我的代码如下所示：
//Initialize Global array variable title_char_cnt_array to char[26]
char title_char_cnt_array[26];
//Initialize SearchTitle array
char *SearchTitle[6] = { "uuul","dule","speed","spede","deul","cars" };
char *Compute_HashMapKey_for_each_title(char title[]) {
//char *T;
//T = title;
Get_Individual_Character_Frequency_For_Each_Title(title);
//Initialize alphabets array to char and assign a to z
//Initialize HashMapKey to char
char *HashMapKy;
HashMapKy = malloc(sizeof(char));
char default_str[] = { "0#" };
char str[50];
char ash[] = { "#" };
int i;
//Create HashMapKey by appending 0# to HashMapKey if a particular alphabet isn't in title or count_of_alphabet plus # if the alphabet is in title (the format is 1#0#1#0#1#0#0#0#0#0#0#0#0#0#1#0#0#2#0#2 ... #1#0#0# for this title: Extractor for e.g)
for (i = 0; i < 26; i++) {
if (title_char_cnt_array[i] == 0) {
//HashMapKey = HashMapKey . '0#';
strcat(HashMapKy,default_str);
} else {
//First convert character frequency count to string
sprintf(str,"%d",title_char_cnt_array[i]);
//concat # to str
strcat(str,ash);
//HashMapKey =. title_char_cnt_array[i].'#';
strcat(HashMapKy,str);
}//end if
}//End For
return HashMapKy;
}
void Get_Individual_Character_Frequency_For_Each_Title(char Title[]) {
int Title_Size;
//get size of Title
Title_Size = strlen(Title);
int x,j;
//Initialize current_char to char for character comparison in title_array
char current_char;
char Alphabets[][1] = { "a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z" };
//Foreach character in title array,calculate individual character frequency here
for (x = 0; x < Title_Size; x++) {
//Initialize current_char_cnt to 0
int current_char_cnt = 1;
current_char = *(Title + x);//retrieve each character of Title array
for (j = x; j < Title_Size; j++) {
if (current_char == *(Title + j + 1)) {
//increment current_char_cnt
current_char_cnt++;
}//End If
}
/*Insert current_char_cnt in title_char_cnt_array against index - index no. represents position of char in alphabetical order*/
if (current_char == Alphabets[0][0])
if (title_char_cnt_array[0] == 0)//if no prevIoUs value inserted,then insert
title_char_cnt_array[0] = current_char_cnt;
if (current_char == Alphabets[1][0])
if (title_char_cnt_array[1] == 0)
title_char_cnt_array[1] = current_char_cnt;
if (current_char == Alphabets[2][0])
if (title_char_cnt_array[2] == 0)
title_char_cnt_array[2] = current_char_cnt;
if (current_char == Alphabets[3][0])
if (title_char_cnt_array[3] == 0)
title_char_cnt_array[3] = current_char_cnt;
if (current_char == Alphabets[4][0])
if (title_char_cnt_array[4] == 0)
title_char_cnt_array[4] = current_char_cnt;
if (current_char == Alphabets[5][0])
if (title_char_cnt_array[5] == 0)
title_char_cnt_array[5] = current_char_cnt;
if (current_char == Alphabets[6][0])
if (title_char_cnt_array[6] == 0)
title_char_cnt_array[6] = current_char_cnt;
if (current_char == Alphabets[7][0])
if (title_char_cnt_array[7] == 0)
title_char_cnt_array[7] = current_char_cnt;
if (current_char == Alphabets[8][0])
if (title_char_cnt_array[8] == 0)
title_char_cnt_array[8] = current_char_cnt;
if (current_char == Alphabets[9][0])
if (title_char_cnt_array[9] == 0)
title_char_cnt_array[9] = current_char_cnt;
if (current_char == Alphabets[10][0])
if (title_char_cnt_array[10] == 0)
title_char_cnt_array[10] = current_char_cnt;
if (current_char == Alphabets[11][0])
if (title_char_cnt_array[11] == 0)
title_char_cnt_array[11] = current_char_cnt;
if (current_char == Alphabets[12][0])
if (title_char_cnt_array[12] == 0)
title_char_cnt_array[12] = current_char_cnt;
if (current_char == Alphabets[13][0])
if (title_char_cnt_array[13] == 0)
title_char_cnt_array[13] = current_char_cnt;
if (current_char == Alphabets[14][0])
if (title_char_cnt_array[14] == 0)
title_char_cnt_array[14] = current_char_cnt;
if (current_char == Alphabets[15][0])
if (title_char_cnt_array[15] == 0)
title_char_cnt_array[15] = current_char_cnt;
if (current_char == Alphabets[16][0])
if (title_char_cnt_array[16] == 0)
title_char_cnt_array[16] = current_char_cnt;
if (current_char == Alphabets[17][0])
if (title_char_cnt_array[17] == 0)
title_char_cnt_array[17] = current_char_cnt;
if (current_char == Alphabets[18][0])
if (title_char_cnt_array[18] == 0)
title_char_cnt_array[18] = current_char_cnt;
if (current_char == Alphabets[19][0])
if (title_char_cnt_array[19] == 0)
title_char_cnt_array[19] = current_char_cnt;
if (current_char == Alphabets[20][0])
if (title_char_cnt_array[20] == 0)
title_char_cnt_array[20] = current_char_cnt;
if (current_char == Alphabets[21][0])
if (title_char_cnt_array[21] == 0)
title_char_cnt_array[21] = current_char_cnt;
if (current_char == Alphabets[22][0])
if (title_char_cnt_array[22] == 0)
title_char_cnt_array[22] = current_char_cnt;
if (current_char == Alphabets[23][0])
if (title_char_cnt_array[23] == 0)
title_char_cnt_array[23] = current_char_cnt;
if (current_char == Alphabets[24][0])
if (title_char_cnt_array[24] == 0)
title_char_cnt_array[24] = current_char_cnt;
if (current_char == Alphabets[25][0])
if (title_char_cnt_array[25] == 0)
title_char_cnt_array[25] = current_char_cnt;
}//End For
}
int main() {
int i;
//Foreach element in title_char_cnt_array,assign an in value of -1
for (i = 0; i < 26; i++)
title_char_cnt_array[i] = 0;
//Initialize HashMap array
struct node *HashMap[9];
int HM_indx = 0;
for (HM_indx = 0; HM_indx < 9; HM_indx++)
HashMap[HM_indx] = NULL;
int sz = 6; //6 titles to insert in hashmap
//Initialize SearchTitle array
//char *SearchTitle[6] = { "uuul","cars" };
char *HMKey;
int x;
for (x = 0; x < sz; x++) {
HMKey = Compute_HashMapKey_for_each_title(SearchTitle[x]);
//printf("%s\n",HMKey);
Insert_Title_To_HashMap_Using_HashMapKey(x,HMKey,HashMap);
}
free(HMKey);
return 0;
}
我期望 Compute_HashMapKey_for_each_title(SearchTitle[x]) 在 HMKey 函数中返回 main 的是：
HashMapKey="0#0#0#0#0#0#0#0#0#0#0#1#0#0#0#0#0#0#0#0#3#0#0#0#0#0#"
但我使用调试器看到的是：
HashMapKey=0xb41700 "À",'«' <repeats 16 times>,"þîþîþîþîþîþîþîþ0#0#0#0#0#0#0#0#0#0#0#1#0#0#0#0#0#0#0#0#3#0#0#0#0#0#"
从main函数中可以看出，一旦我得到HMKey；我将它传递给函数 Insert_Title_To_HashMap_Using_HashMapKey(x,HashMap)，然后将我期望的字符串："0#0#0#0#0#0#0#0#0#0#0#1#0#0#0#0#0#0#0#0#3#0#0#0#0#0#" 分解为单个字符，将每个字符转换为它的 ASCII 数字，然后求和。所以我希望看到 0 作为第一个字符，# 作为第二个字符，0 作为第三个字符等等，但是我看到使用调试器的第一个字符是À 是 Compute_HashMapKey_for_each_title(SearchTitle[x]) 返回值中地址后的第一个字符，返回到 HMKey。
在这种情况下，即使我预期的 strlen 应该是 52，但我看到的是：84。
我不知道发生了什么，请提供任何帮助，我们将不胜感激。
解决方法
HashMapKy = malloc(sizeof(char));
您只为单个字符分配空间。 C 语言中的数组或内存不是动态的，您不能通过附加到它们来“扩展”内存或数组。
此外，strcat 函数要求两个字符串都是以空字符结尾的字符串。由于 malloc 函数无论如何都不会初始化它分配的内存，它的内容将是不确定（最好将其视为垃圾或随机）。它的第一个位置不太可能包含零（空终止符）。
您应该将大小分配为 HashMapKy = (char*) malloc (sizeof(char) * 25);
Compute_HashMapKey_for_each_title 有一个主要问题：你没有为哈希字符串分配足够的空间，malloc(sizeof(char)) 分配了一个字节。
字符串可以是 5 加上空终止符的 26 倍（如果 title_char_cnt_array 是 char 的数组，则为 5 个字节，但如果将其更改为 int，则为 12 个字节）。我建议使用本地数组并使用 strdup() 返回分配的副本：
char *Compute_HashMapKey_for_each_title(char title[]) {
char buf[26 * 12 + 1];
int pos = 0;
Get_Individual_Character_Frequency_For_Each_Title(title);
// Create HashMapKey by appending the number of occurrences for each character
// followed by a `#` char.
for (int i = 0; i < 26; i++) {
pos += sprintf(buf + pos,"%d#",title_char_cnt_array[i]);
}
return strdup(buf);
}
函数Get_Individual_Character_Frequency_For_Each_Title可以大大简化：
void Get_Individual_Character_Frequency_For_Each_Title(char Title[]) {
const char *alphabet = "abcdefghijklmnopqrstuvwyxz";
for (int i = 0; i < 26; i++) {
title_char_cnt_array[i] = 0;
}
for (int i = 0; Title[i] != '\0'; i++) {
char *p = strchr(alphabet,Title[i]);
if (p != NULL) {
title_char_cnt_array[p - alphabet] += 1;
}
}
}
如果您可以假设系统使用 ASCII 字符集，则该功能可以更简单：
void Get_Individual_Character_Frequency_For_Each_Title(char Title[]) {
for (int i = 0; i < 26; i++) {
title_char_cnt_array[i] = 0;
}
for (int i = 0; Title[i] != '\0'; i++) {
char c = Title[i];
if (c >= 'a' && c <= 'z') {
title_char_cnt_array[c - 'a'] += 1;
}
}
}
请注意，title_char_cnt_array 应作为参数传递，并且应具有大于 char 的整数类型。