这个问题是this question的延续。
这是代码：
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int ch;
char *ptrChFromFile;
char **ptrWords;
int strSize = 1;
int i;
int j = 0;
int numberOfWords = 1;
ptrChFromFile = malloc(sizeof(char));
if (ptrChFromFile == NULL)
{
puts("COULDN'T ALLOICATE MEMORY");
exit(EXIT_FAILURE);
}
while ((ch = getchar()) != '\n')
{
ptrChFromFile = realloc(ptrChFromFile, (strSize+1) * sizeof(char));
if (ptrChFromFile == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
if (ch == ' ')
{
numberOfWords++;
}
ptrChFromFile[strSize] = ch;
strSize++;
}
ptrChFromFile[strSize] = 0;
ptrWords = malloc(sizeof(char*) * numberOfWords); //creates number of slots in ptr
if (ptrWords == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
for (i = 0; i < numberOfWords; i++) // allocates number of bytes in each slot.
{
ptrWords[i] = malloc(sizeof(char*)* strSize);
if (ptrWords[i] == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
}
for (i = 0; i < strSize; i++)
{
if (ptrChFromFile[i] != ' ')
{
ptrWords[j] = &ptrChFromFile[i];
}
else
{
ptrWords[j] = 0;
j++;
}
}
for (i = 0; i < numberOfWords; i++) // free's each slot in ptrWords
{
free(ptrWords[i]);
}
free(ptrChFromFile);
free(ptrWords);
return 0;
}
我试图动态分配我的双字符指针ptrWords。请允许我解释一下我的思考过程：
ptrWords = malloc(sizeof(char*) * numberOfWords); //creates number of slots in ptr
这会在ptrWords中创建槽数（索引）。所以如果我有3个字，ptrWords应该是这样的：
ptrWords [索引0]
ptrWords [索引1]
ptrWords [索引2]
for (i = 0; i < numberOfWords; i++) // allocates number of bytes in each slot.
{
ptrWords[i] = malloc(sizeof(char*)* strSize);
if (ptrWords[i] == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
}
这个for循环为ptrWords中的每个槽分配内存，等于输入文件中的字符总数。因此，如果输入文件总共有26个字符，那么ptrWords中的每个插槽将分配26个字节。
ptrWords [index 0]有26个字节的内存
ptrWords [索引1]有26个字节的内存
ptrWords [索引2]有26个字节的内存
我认为我对ptrWords的记忆分配是正确的，但我不确定。
for (i = 0; i < strSize; i++)
{
if (ptrChFromFile[i] != ' ')
{
ptrWords[j] = &ptrChFromFile[i];
}
else
{
ptrWords[j] = 0;
j++;
}
}
这个for循环应该从ptrChFromFile获取字符并将它们作为单独的单词存储在ptrWords中。我的循环逻辑如下：
1）只要ch不等于空格，取该字符并将其存储在ptrWords的第一个位置（索引0）。
2）如果ch确实等于空格，则在其位置放置一个终止字符（'\ 0'）然后将j递增1以移动到ptrWords中的下一个索引以存储下一个单词。
我已经使用调试器来逐步完成代码，但我仍然无法弄清楚什么是错误的，所以任何帮助都会受到赞赏。
谢谢
我的实施：
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int ch;
char *ptrChFromFile;
char **ptrWords;
int strSize = 1;
int i;
int j = 0;
int k = 0;
int numberOfWords = 1;
ptrChFromFile = malloc(sizeof(char));
if (ptrChFromFile == NULL)
{
puts("COULDN'T ALLOCATE MEMORY");
exit(EXIT_FAILURE);
}
while ((ch = getchar()) != '\n')
{
ptrChFromFile = realloc(ptrChFromFile, (strSize+1) * sizeof(char));
if (ptrChFromFile == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
if (ch == ' ')
{
numberOfWords++;
}
ptrChFromFile[strSize] = ch;
strSize++;
}
ptrChFromFile[strSize] = 0;
ptrWords = malloc(sizeof(char*) * numberOfWords); //creates number of slots in ptrWords
for (i = 0; i < numberOfWords; i++) // allocates number of bytes in each slot.
{
ptrWords[i] = malloc(sizeof(char*)* strSize);
if (ptrWords[i] == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
}
if (ptrWords == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
for (i = 0; i < strSize; i++)
{
if (ptrChFromFile[i] != ' ')
{
ptrWords[j][k++] = ptrChFromFile[i];
}
else
{
ptrWords[j][k] = 0;
ptrWords[j] = realloc(ptrWords[j], k+1);
j++;
k = 0;
}
}
printf("%s", ptrWords[0]);
free(ptrChFromFile);
free(ptrWords);
return 0;
}
样本输入：“嘿那里”
输出：嘿那里
嘿
当前版本的代码：
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int getStrLength(char *word)
{
int lengthOfWord = 0;
int i;
for (i = 0; word[i] != 0; i++)
{
lengthOfWord++;
}
return lengthOfWord;
}
int compareWords(char *firstWord, char *secondWord)
{
while (*firstWord && *firstWord == *secondWord)
{
firstWord++;
secondWord++;
}
return *firstWord - *secondWord;
}
int main(void)
{
int ch;
char *ptrChFromFile;
char **ptrWords;
char **ptrCrunchWord;
int strSize = 0;
int i;
int j = 0;
int k = 0;
int numberOfWords = 0;
int defaultWordLength = 6;
srand(time(0)); // Use current time as seed for random generator
ptrChFromFile = malloc(sizeof(char));
if (ptrChFromFile == NULL)
{
puts("COULDN'T ALLOCATE MEMORY");
exit(EXIT_FAILURE);
}
while ((ch = getchar()) != '\n') // this reads in chars from file to ch variable
{
ptrChFromFile = realloc(ptrChFromFile, (strSize+1) * sizeof(char));
if (ptrChFromFile == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
if (ch == ' ')
{
numberOfWords++;
}
ptrChFromFile[strSize] = ch;
strSize++;
}
numberOfWords++;
ptrChFromFile[strSize] = 0;
ptrWords = malloc(sizeof(char*) * numberOfWords); //creates number of slots in ptrWords
if (ptrWords == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
for (i = 0; i < numberOfWords; i++) // allocates number of bytes in each slot.
{
ptrWords[i] = malloc(strSize);
if (ptrWords[i] == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
}
for (i = 0; i < strSize; i++) // This inserts words in ptrWords separated by spaces.
{
if (ptrChFromFile[i] != ' ')
{
ptrWords[j][k++] = ptrChFromFile[i];
}
else
{
ptrWords[j][k] = 0;
ptrWords[j] = realloc(ptrWords[j], k+1);
j++;
k = 0;
}
}
// terminate and resize last word
ptrWords[j][k] = 0;
ptrWords[j] = realloc(ptrWords[j], k+1);
j = 0;
k = 0;
// crunchWord code starts here:
ptrCrunchWord = malloc(sizeof(char*));
ptrCrunchWord[0] = malloc(strSize);
if (ptrCrunchWord == NULL || ptrCrunchWord[0] == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
for (i = 0; i < numberOfWords; i++)
{
int randomIndex = rand() % numberOfWords;
if (compareWords(ptrCrunchWord[i], ptrWords[randomIndex]) != 0)
{
if (getStrLength(ptrWords[randomIndex]) >= defaultWordLength)
{
ptrCrunchWord[i] = ptrWords[randomIndex]; // main problem here
}
}
}
printf("The crunch word is: %s", ptrCrunchWord[0]);
for (i = 0; i < numberOfWords; i++) // Free's allocated memory from all pointers
{
free(ptrWords[i]);
}
free(ptrChFromFile);
free(ptrWords);
free(ptrCrunchWord[0]);
free(ptrCrunchWord);
return 0;
}
这是最新的代码。我需要做的最后一件事是在ptrCrunchWord中存储大于或等于6的所有单词。我的主要问题是在ptrCrunchWord [0]中为最终的紧缩字分配空间并将单词存储在索引0中。我只为元素分配空间，因为ptrCrunchWord中只存储一个单词。我写了两个方法，一个检查每个单词的长度，另一个方法比较两个单词，看看它们是否相同。最后，我需要打印没有空格的紧缩字。
谢谢
这个循环错了：
for (i = 0; i < strSize; i++)
{
if (ptrChFromFile[i] != ' ')
{
ptrWords[j] = &ptrChFromFile[i];
}
else
{
ptrWords[j] = 0;
j++;
}
}
你不应该重新分配ptrWords[j]，你应该复制到你在前一个循环中分配的内存中。您需要另一个变量k来保存您在目标数组中分配的索引。
int k = 0;
for (i = 0; i < strSize; i++)
{
if (ptrChFromFile[i] != ' ')
{
ptrWords[j][k++] = ptrChFromFile[i];
}
else
{
ptrWords[j][k] = 0;
j++;
k = 0;
}
}
你也为你分配给ptrWords的内存量过分了。每个单词都有与文件整个大小一样多的字符。到达每个单词的末尾后，在分配ptrWords[j][k] = 0之后，您可以将该分配缩小到单词的大小：
ptrWords[j] = realloc(ptrWords[j], k+1);
另一个问题是你初始化了strSize = 1;。这导致您将输入的第一个字符放入ptrChFromFile[1]而不是ptrChFromFile[0]，因此第一个单词无法正确复制。它应该初始化为int strSize = 0。但是要调整此更改，您需要将所有ptrChFromFile分配增加1个字符（或者在末尾执行另一个realloc以为尾随空值添加空间）。
当你为ptrWords[i]分配内存时，你不应该乘以sizeof(char *)。 ptrWords是一个指针数组，ptrWords[i[是char的数组。
完成读取ptrChFromFile初始输入的循环后，需要增加numberOfWords。否则你不会计算换行前的最后一个字。
你不应该在最后删除循环，释放所有ptrWords[i]。你用malloc分配的任何东西都需要被释放。
这是工作版本：
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int ch;
char *ptrChFromFile;
char **ptrWords;
int strSize = 0;
int i;
int j = 0;
int k = 0;
int numberOfWords = 1;
ptrChFromFile = malloc(2);
if (ptrChFromFile == NULL)
{
puts("COULDN'T ALLOCATE MEMORY");
exit(EXIT_FAILURE);
}
while ((ch = getchar()) != '\n')
{
ptrChFromFile = realloc(ptrChFromFile, (strSize+2));
if (ptrChFromFile == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
if (ch == ' ')
{
numberOfWords++;
}
ptrChFromFile[strSize] = ch;
strSize++;
}
numberOfWords++; // increment for last word
ptrChFromFile[strSize] = 0;
ptrWords = malloc(sizeof(char*) * numberOfWords); //creates number of slots in ptrWords
for (i = 0; i < numberOfWords; i++) // allocates number of bytes in each slot.
{
ptrWords[i] = malloc(strSize);
if (ptrWords[i] == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
}
if (ptrWords == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
for (i = 0; i < strSize; i++)
{
if (ptrChFromFile[i] != ' ')
{
ptrWords[j][k++] = ptrChFromFile[i];
}
else
{
ptrWords[j][k] = 0;
ptrWords[j] = realloc(ptrWords[j], k+1);
j++;
k = 0;
}
}
printf("%s\n", ptrWords[0]);
for (i = 0; i < strSize; i++) {
free(ptrWords[i]);
}
free(ptrChFromFile);
free(ptrWords);
return 0;
}
我将尝试显示更像您的初始版本的版本。
我将跳过阅读文件的部分。当然，需要应用与Barmar提到的strSize相关的修复。此代码在读取文件后开始。
ptrChFromFile[strSize] = 0;
ptrWords = malloc(sizeof(char*) * numberOfWords); //creates number of slots in ptr
if (ptrWords == NULL)
{
puts("failed to allocate memory");
exit(EXIT_FAILURE);
}
#define MIN_LENGTH 6
int start = 0, end = 0;
numWords = 0; // Start counting again. Only handle words long enough.
for (i = 0; i < strSize; i++) // Walk the inital array again
{
if (ptrChFromFile[i] == ` `)
{
end = i;
if (end - start >= MIN_LENGTH)
{ // Found a word? Store address and terminate.
ptrWords = &ptrChFromFile[start];
ptrChFromFile[i] = 0;
numWords ++;
}
// Words that are too short are ignored
// Also if a second space follows, no new word is counted...
// Prepare for new word starting at next position.
start = end = i+1;
}
}
// Maybe one more word without a space afterwards?
end = i;
if (end - start >= MIN_LENGTH)
{ // Found a word? Store address and terminate.
ptrWords = &ptrChFromFile[start];
// ptrChFromFile[i] = 0; This word is already terminated.
numWords ++;
}
ptrWords = realloc(sizeof(char*) * numberOfWords); // Reduce size to only hold long words
// Decide number n how many words shall be concatenated
// Use scanf or any other mechanism...
int n = numWords / 2;
为了选择单词，我将使用数组来仅保存每个单词的索引。它用索引0..n-1初始化。对于每个选定的单词，我将索引移动到数组中的第一个位置，并将（前）第一个元素放到所选位置。在此之后，前n个元素保持随机索引值。随着每个步骤中随机选择的范围减小，不可能存在重复。不需要比较单词。
// Create an array to hold the indices of chosen words.
int selectedWords[n];
for (i = 0; i < n; i++)
selectedWords[i] = i;
// Select n words, store index.
srand(time(0));
for (i = 0; i < n; i++)
{
// Pick random element 0..n
int elem = rand()%(n-i);
int temp;
temp = selectedWords[i+elem];
selectedWords[i+elem] = selectedWords[i];
selectedWords[i] = temp;
}
// This first n entries hold the selected words.
// How long will it be in the end?
size_t len = 0;
for (i = 0; i < n; i++)
{
len += strlen(ptrWords[selectedWords[n]]);
}
// Get memory for final result...
char *resultWord = malloc(len+1);
// TODO: check for NULL
resultWord[0] = 0;
for (i = 0; i < n; i++)
{
strcat(resultWord, ptrWords[selectedWords[n]]);
}
printf("%s\n", resultWord)
free(ptrChFromFile);
free(ptrWords);
free(resultWord);
return 0;
}
代码未编译或测试。