我一直有这个问题围绕着我已经给予的一些代码。这个问题在menu_add_book函数或read_line函数中的某个地方，当我运行它时它编译没有问题我可以使用输入文件输入第一个选项，但是当涉及到标题时出现分段错误。我很确定这与分配内存有关，但是对于我的生活无法解决什么问题，如果有人可以帮我解释一下，那么你将成为一个生命保护者。 我的代码如下
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#define MAX_TITLE_LENGTH 100
#define MAX_AUTHOR_LENGTH 100
/* Book structure */
struct Book
{
/* Book details */
char title[MAX_TITLE_LENGTH+1]; /* name string */
char author[MAX_AUTHOR_LENGTH+1]; /* job string */
int year; /* year of publication */
/* pointers to left and right branches pointing down to next level in
the binary tree */
struct Book *left, *right;
};
/* tree of books, initialized to NULL. */
static struct Book *book_tree = NULL;
/* read_line():
*
* Read line of characters from file pointer "pf", copying the characters
* into the "line" string, up to a maximum of "max_length" characters, plus
* one for the string termination character '\0'. Reading stops upon
* encountering the end-of-line character '\n', for which '\0' is substituted
* in the string. If the end of file character EOF is reached before the end
* of the line, the failure condition (-1) is returned. If the line is longer
* than the maximum length "max_length" of the string, the extra characters
* are read but ignored. Success is returned (0) on successfully reading
* a line.
*/
static int read_line ( FILE *pf, char *line, int max_length )
{
int i;
char ch;
/* initialize index to string character */
i = 0;
/* read to end of line, filling in characters in string up to its
maximum length, and ignoring the rest, if any */
for(;;)
{
/* read next character */
ch = fgetc(pf);
/* check for end of file error */
if ( ch == EOF )
return -1;
/* check for end of line */
if ( ch == '\n' )
{
/* terminate string and return */
line[i] = '\0';
return 0;
}
/* fill character in string if it is not already full*/
if ( i < max_length )
line[i++] = ch;
}
/* the program should never reach here */
return -1;
}
/* read_string():
*
* Reads a line from the input file pointer "pf", starting with the "prefix"
* string, and filling the string "string" with the remainder of the contents
* of the line. If the start of the line does not match the "prefix" string,
* the error condition (-1) is returned. Having read the prefix string,
* read_string() calls read_line() to read the remainder of the line into
* "string", up to a maximum length "max_length", and returns the result.
*/
static int read_string ( FILE *pf,
char *prefix, char *string, int max_length )
{
int i;
/* read prefix string */
for ( i = 0; i < strlen(prefix); i++ )
if ( fgetc(pf) != prefix[i] )
/* file input doesn't match prefix */
return -1;
/* read remaining part of line of input into string */
return ( read_line ( pf, string, max_length ) );
}
/* menu_add_book():
*
* Add new book to database
*/
static void menu_add_book(void)
{
FILE *pf = NULL;
char *line = NULL;
int max_length = 100;
int year;
struct Book *new = NULL;
new = (struct Book *) malloc ( sizeof(struct Book) );
fprintf(stderr,"\nEnter Title:");
read_line ( pf, line, max_length );
fprintf(stderr,"\nEnter Author:");
read_line ( pf, line, max_length );
fprintf(stderr,"\nEnter Year:\n");
scanf( "%i", &year);
}
/* menu_print_database():
*
* Print database of books to standard output in alphabetical order of title.
*/
static void menu_print_database(void)
{
/* fill in the code here in part 1, and add any extra functions you need */
}
/* menu_get_book_details():
*
* Get details of book from database.
*/
static void menu_get_book_details(void)
{
/* fill in the code here in part 2, and add any extra functions you need */
}
/* menu_delete_book():
*
* Delete new book from database.
*/
static void menu_delete_book(void)
{
/* fill in the code here in part 2, and add any extra functions you need */
}
/* read file containing database of books */
static void read_book_database ( char *file_name )
{
/* fill in the code here in part 3, and add any extra functions you need */
}
/* get_tree_depth():
*
* Recursive function to compute the number of levels in a binary tree.
*/
static int get_tree_depth ( struct Book *book, int level )
{
int level1, level2;
/* return with the current level if we've reached the bottom of this
branch */
if ( book == NULL ) return level;
/* we need to go to the next level down */
level++;
/* count the number of levels down both branches */
level1 = get_tree_depth ( book->left, level );
level2 = get_tree_depth ( book->right, level );
/* return the depth of the deepest branch */
if ( level1 > level2 ) return level1;
else return level2;
}
/* menu_print_tree():
*
* Print tree to standard output. You can use this function to print out the
* tree structure for debugging purposes. It is also used by the testing
* software to check that the tree is being built correctly.
*
* The first letter of the title of each book is printed.
*/
static void menu_print_tree(void)
{
int no_levels, level, size, i, j, k;
struct Book **row;
/* find level of lowest node on the tree */
no_levels = get_tree_depth ( book_tree, 0 );
/* abort if database is empty */
if ( no_levels == 0 ) return;
/* compute initial indentation */
assert ( no_levels < 31 );
row = (struct Book **) malloc((1 << (no_levels-1))*sizeof(struct Book *));
row[0] = book_tree;
printf ( "\n" );
for ( size = 1, level = 0; level < no_levels; level++, size *= 2 )
{
/* print books at this level */
for ( i = 0; i < size; i++ )
{
if ( i == 0 )
for ( j = (1 << (no_levels - level - 1)) - 2; j >= 0; j-- )
printf ( " " );
else
for ( j = (1 << (no_levels - level)) - 2; j >= 0; j-- )
printf ( " " );
if ( row[i] == NULL )
printf ( " " );
else
printf ( "%c", row[i]->title[0] );
}
printf ( "\n" );
if ( level != no_levels-1 )
{
/* print connecting branches */
for ( k = 0; k < ((1 << (no_levels - level - 2)) - 1); k++ )
{
for ( i = 0; i < size; i++ )
{
if ( i == 0 )
for ( j = (1 << (no_levels - level - 1))-3-k; j >= 0; j-- )
printf ( " " );
else
for ( j = (1 << (no_levels - level)) - 4 - 2*k; j >= 0; j-- )
printf ( " " );
if ( row[i] == NULL || row[i]->left == NULL )
printf ( " " );
else
printf ( "/" );
for ( j = 0; j < 2*k+1; j++ )
printf ( " " );
if ( row[i] == NULL || row[i]->right == NULL )
printf ( " " );
else
printf ( "\\" );
}
printf ( "\n" );
}
/* adjust row of books */
for ( i = size-1; i >= 0; i-- )
{
row[2*i+1] = (row[i] == NULL) ? NULL : row[i]->right;
row[2*i] = (row[i] == NULL) ? NULL : row[i]->left;
}
}
}
free(row);
}
/* codes for menu */
#define ADD_CODE 0
#define DETAILS_CODE 1
#define DELETE_CODE 2
#define PRINT_CODE 3
#define TREE_CODE 4
#define EXIT_CODE 5
int main ( int argc, char *argv[] )
{
/* check arguments */
if ( argc != 1 && argc != 2 )
{
fprintf ( stderr, "Usage: %s [<database-file>]\n", argv[0] );
exit(-1);
}
/* read database file if provided, or start with empty database */
if ( argc == 2 )
read_book_database ( argv[1] );
for(;;)
{
int choice, result;
char line[301];
/* print menu to standard error */
fprintf ( stderr, "\nOptions:\n" );
fprintf ( stderr, "%d: Add new book to database\n", ADD_CODE );
fprintf ( stderr, "%d: Get details of book\n", DETAILS_CODE );
fprintf ( stderr, "%d: Delete book from database\n", DELETE_CODE );
fprintf ( stderr, "%d: Print database to screen\n", PRINT_CODE );
fprintf ( stderr, "%d: Print tree\n", TREE_CODE );
fprintf ( stderr, "%d: Exit database program\n", EXIT_CODE );
fprintf ( stderr, "\nEnter option: " );
if ( read_line ( stdin, line, 300 ) != 0 ) continue;
result = sscanf ( line, "%d", &choice );
if ( result != 1 )
{
fprintf ( stderr, "corrupted menu choice\n" );
continue;
}
switch ( choice )
{
case ADD_CODE: /* add book to database */
menu_add_book();
break;
case DETAILS_CODE: /* get book details from database */
menu_get_book_details();
break;
case DELETE_CODE: /* delete book from database */
menu_delete_book();
break;
case PRINT_CODE: /* print database contents to screen
(standard output) */
menu_print_database();
break;
case TREE_CODE: /* print tree to screen (standard output) */
menu_print_tree();
break;
/* exit */
case EXIT_CODE:
break;
default:
fprintf ( stderr, "illegal choice %d\n", choice );
break;
}
/* check for exit menu choice */
if ( choice == EXIT_CODE )
break;
}
return 0;
}
答案 0 :(得分：2)
您已将line初始化为：
char *line = NULL;
但你没有为它分配任何记忆。
添加
line = malloc(max_length+1);
read_line之前。
答案 1 :(得分：1)
您拥有char* line = NULL，然后为new动态分配内存。
但是，您在函数line中传递了read_line as参数，然后尝试使用i-th运算符访问其[]元素，从而获得了SEG。故障。
为了解决这个问题，你可以这样做：
char *line = NULL;
int max_length = 100;
line = malloc( (max_length + 1) * sizeof(char) ); // +1 for the null terminator
此外，在stderr中打印菜单并不常见。 stderr是错误流。菜单不是错误。
我会写，而不是：
fprintf ( stderr, "\nOptions:\n" );
此
fprintf ( stdout, "\nOptions:\n" ); // or use printf
您可能还想阅读：Why not casting the result of malloc in C?
另一个更重要的logical error，接近导致您的细分错误的错误。
您没有初始化文件指针pf，但是您希望在read_line中读取它。
FILE *pf = NULL; // the file pointer
char *line = NULL; // fix the initial logical error
int max_length = 100;
line = malloc(max_length + 1);
int year;
struct Book *new = NULL;
new = (struct Book *) malloc ( sizeof(struct Book) );
fprintf(stderr,"\nEnter Title:");
read_line ( pf, line, max_length ); // Here, you pass pf uninitialized
然后在read_line()，您可以：
char ch; // you may want to change that in: int char;
ch = fgetc(pf);
那么，文件指针设置在哪里？无处！
而且，你将你的变量命名为pf，但它是一个文件指针，所以fp会更好，恕我直言。
也许还有其他错误，但我认为现在已经足够了。