我对C很新，并且这是一个练习。代码在命中运行时错误之前编译并运行Abort trap：6。我在第二次调用第二次递归调用会议j时越过边界跟踪错误到计数器i < last_line。我无法在代码中看到错误。快速排序不是我特别熟悉的方法;任何人都可以帮我找到错误吗？
我所喂的名字是：
James
Janet
James
Rosie
Dave
这是我的代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void quicksort(char **array, int first_line, int last_line) ;
int main(int argc, char* argv[])
{
int i = 0 ;
int j = 0 ;
int line_count = 0 ;
int line_number = 20 ;
char *lines[20] ;
//char temp[BUFSIZ] ;
FILE *foutptr ;
FILE *finptr ;
finptr = fopen("names.txt", "r") ;
if(finptr == NULL)
{
perror("ERROR: input file pointer") ;
return 1 ;
}
foutptr = fopen("sorted.txt", "w") ;
if(foutptr == NULL)
{
perror("ERROR: output file pointer") ;
return 1 ;
}
lines[i] = malloc(BUFSIZ) ;
while(fgets(lines[i],BUFSIZ,finptr) && i < line_number)
{
printf("Element %d is the name %s.\n", i, lines[i]) ;
i++ ;
lines[i] = malloc(BUFSIZ) ;
}
printf("TEST %s.\n", *(lines+1)) ;
line_count = i ;
i = 0 ;
char **all_lines = lines ;
quicksort(all_lines, 0, line_count-1) ;
for(j = 0 ; j < line_count ; j++)
{
fprintf(foutptr, "%s", lines[j]) ;
}
return 0 ;
}
void quicksort(char **array, int first_line, int last_line)
{
int i = 0, j = 0, x = 0, pivot = (first_line + last_line)/2 ;
char temp[100] ;
i = first_line ;
j = last_line ;
if(last_line - first_line < 1)
{
return ;
}
printf("first_line = %d so i = %d. last line = %d so j = %d. The pivot is %d \n", first_line, i, last_line, j, pivot) ;
while(i <= j)
{
/* While array[i] proceeds the pivot alphabetically and is less than array[j] move through the array. This deals with first mismatching letter of first string is less than the second
in ASCII character numbers i.e. if earlier in the alphabet as ASCII chartcters earlier in the alphabet have a lower numerical id */
while(strcmp(array[i], array[pivot]) < 0 && i < last_line)
{
printf("No swapping In while 1, comparing %s and %s with strcmp = %d. \n", array[i], array[pivot], strcmp(array[i], array[pivot])) ;
printf("%d. \n", i) ;
i++ ;
}
/* While array[j] follows the pivot alphabetically and is greater than array[i] move through the array. This deals with the first mismatching letter of first string compared to the second is greater in number id i.e. the ASCII character code is bigger in the first so it is latter in the alphabet */
while(strcmp(array[j], array[pivot]) > 0 && j > first_line)
{
printf("No swapping In while 2, comparing %s and %s with strcmp = %d. \n", array[j], array[pivot], strcmp(array[j], array[pivot])) ;
printf("%d. \n", j) ;
j-- ;
}
// Swap if the conditions above are not met
if(i <= j)
{
printf("%s\n","SWAPPING") ;
printf("Array[%d] = %s, Array[%d] = %s", i, array[i], j, array[j]) ;
strcpy(temp,array[i]) ;
strcpy(array[i], array[j]) ;
strcpy(array[j],temp) ;
printf("Array[%d] = %s, Array[%d] = %s", i, array[i], j, array[j]) ;
i++ ;
j-- ;
}
}
if(first_line < j)
{
printf("Recursive call 1: Lower bound = %d, Upper bound = %d\n", first_line, j) ;
for(x = 0 ; x < last_line + 1 ; x++)
{
printf("Array[%d]: %s \n", x, array[x]) ;
}
quicksort(array, first_line, j) ;
}
x = 0 ;
if(i < last_line)
{
printf("Recursive call 2: Lower bound = %d, Upper bound = %d\n", i, last_line) ;
for(x = 0 ; x < last_line + 1 ; x++)
{
printf("Array[%d]: %s \n", x, array[x]) ;
}
quicksort(array, i, last_line) ;
}
x = 0 ;
return ;
}
答案 0 :(得分：1)
正如评论中已经介绍的那样，我在代码中看不到任何可以解释您声称要观察到的越界索引问题的内容，而且我自己也没有用您的代码和数据来观察它。实际上，您提供的代码似乎不具备您描述的行为的可能性。如果事实上你确实观察到了这样的问题，那么我倾向于猜测它与你实际使用的代码和你提供的代码之间的某些差异有关。
另一方面，正如我在评论中首次提到的那样，你的代码是错误的。构造一个较长的输入是相对容易的，它会排序错误（我在第一次尝试时这样做，没有特别考虑你的实现细节）。我看到的问题是，在分区期间，您使用array[pivot]来引用枢轴元素，从而假设枢轴元素保持在其初始位置。某些输入的某些分区会违反该假设 ，可能会导致数组未正确排序。
另请注意，我强烈建议您直接对数组的元素（指针）执行交换，而不是交换指针所指向的char数组的内容。这不仅会更有效，而且可以更容易地解决您的pivot元素的问题。事实上它是唯一的选择，如果你不能依赖指向所有指向相同大小的分配。
答案 1 :(得分：1)
以下代码包含上述答案和评论中给出的建议。此代码似乎正常工作，但仍不清楚为什么最初收到Abort陷阱6运行时错误。
最终代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void quicksort(char **array, int first_line, int last_line) ;
int main(int argc, char* argv[])
{
int i = 0 ;
int j = 0 ;
int line_count = 0 ;
int line_number = 20 ;
char *lines[100] ;
FILE *foutptr ;
FILE *finptr ;
finptr = fopen("names.txt", "r") ;
if(finptr == NULL)
{
perror("ERROR: input file pointer") ;
return 1 ;
}
foutptr = fopen("sorted.txt", "w") ;
if(foutptr == NULL)
{
perror("ERROR: output file pointer") ;
return 1 ;
}
lines[i] = malloc(BUFSIZ) ;
while(fgets(lines[i],BUFSIZ,finptr) && i < line_number)
{
printf("Element %d is the name %s.\n", i, lines[i]) ;
i++ ;
lines[i] = malloc(BUFSIZ) ;
}
printf("TEST %s.\n", *(lines+1)) ;
line_count = i ;
i = 0 ;
char **all_lines = lines ;
quicksort(all_lines, 0, line_count-1) ;
for(j = 0 ; j < line_count ; j++)
{
fprintf(foutptr, "%s", lines[j]) ;
}
return 0 ;
}
void quicksort(char **array, int first_line, int last_line)
{
int i = 0, j = 0, x = 0i, p = (first_line + last_line)/2 ;
printf("%s \n", array[p]) ;
char pivot[BUFSIZ] ;
char *temp_ptr ;
strcpy(pivot,array[p]) ;
i = first_line ;
j = last_line ;
if(last_line - first_line < 1)
{
return ;
}
printf("first_line = %d so i = %d. last line = %d so j = %d. The pivot is array[%d] \n", first_line, i, last_line, j, p) ;
while(i <= j)
{
/* While array[i] proceeds the pivot alphabetically and is less than array[j] move through the array. This deals with first
mismatching letter of first string is less than the second in ASCII character numbers i.e. if earlier in the alphabet as ASCII
chartcters earlier in the alphabet have a lower numerical id */
while(strcmp(array[i], pivot) < 0 && i < last_line)
{
printf("No swapping In while 1, comparing %s and %s with strcmp = %d. \n", array[i], pivot, strcmp(array[i], pivot)) ;
printf("%d. \n", i) ;
i++ ;
}
/* While array[j] follows the pivot alphabetically and is
greater than array[i] move through the array. This deals with the
first mismatching letter of first string compared to the second
is greater in number id i.e. the ASCII character code is
bigger in the first so it is latter in the alphabet */
while(strcmp(array[j], pivot) > 0 && j > first_line)
{
printf("No swapping In while 2, comparing %s and %s with strcmp = %d. \n", array[j], pivot, strcmp(array[j], pivot)) ;
printf("%d. \n", j) ;
j-- ;
}
// Swap if the conditions above are not met
if(i <= j)
{
printf("%s\n","SWAPPING") ;
printf("Array[%d] = %s, Array[%d] = %s", i, array[i], j,array[j]) ;
temp_ptr = array[i] ; //Here we copy pointers which is eaier to do than copy the array contents and is more efficent.
array[i] = array[j] ;
array[j] = temp_ptr ;
//strcpy(temp,array[i]) ; // This is much less efficent as it copies the contents of the aray not the pointers.
//strcpy(array[i], array[j]) ;
//strcpy(array[j],temp) ;
printf("Array[%d] = %s, Array[%d] = %s", i, array[i], j,array[j]) ;
i++ ;
j-- ;
}
}
if(first_line < j)
{
printf("Recursive call 1: Lower bound = %d, Upper bound = %d\n", first_line, j) ;
for(x = 0 ; x < last_line + 1 ; x++)
{
printf("Array[%d]: %s \n", x, array[x]) ;
}
quicksort(array, first_line, j) ;
}
x = 0 ;
if(i < last_line)
{
printf("Recursive call 2: Lower bound = %d, Upper bound = %d\n", i, last_line) ;
for(x = 0 ; x < last_line + 1 ; x++)
{
printf("Array[%d]: %s \n", x, array[x]) ;
}
quicksort(array, i, last_line) ;
}
x = 0 ;
return ;
}