代码在大多数输入上都能正常工作，但是对于userID来说，很长时间我会遇到分段错误。我的问题是，malloc如何导致分段错误？简单地分配内存不应该导致这种情况。我通过使用printf（）语句找到了问题区域，似乎我的read_line（）函数中的malloc是问题所在，因为第二个“read_line”没有打印，而是在malloc之前的第一个。
谢谢你。 - 克里斯#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#define DELIM " " /* the delimiter */
#define MAX_CHANGE (10.0/86400.0) /* 10kg/day */
/* seconds in a day is 24 hours * 60 minutes * 60 seconds */
#define MEM_OUT printf("%s","out of memory");
/* Defines Node structure. */
struct Node{
char *id;
float weight;
int time;
struct Node *next;
} *head, *p, *t, *last;
/* Constructor which returns a pointer to a new node. */
struct Node * new_node(int time, char *id, float w)
{ /*note malloc returns a pointer */
struct Node *node = (struct Node *)malloc(sizeof(struct Node));
node->time = time;
node->id = (char *)malloc( (strlen(id) + 1) * sizeof(char));
strcpy(node->id, id); //duplicate the id, so new node has own copy.
node->weight = w;
node->next = NULL;
return node;
}
/* reads in line of characters until either a EOF or '\n' is encountered
then places a the terminator '\0' at the end */
char * read_line(FILE *stream)
{
printf("read_line");
char * temp = (char*)malloc(sizeof(char));
printf("read_line");
char * line = (char*)malloc(sizeof(char));
char c;
*line = '\0';
int i = 1;
//strchr()
while( (c = getc(stream)) != EOF && c != '\n')
{
//if(c == EOF) return NULL;
//realloc(line,++i);
strcpy(temp,line);
line = malloc(++i * sizeof(char));
strcpy(line,temp);
temp = malloc(i * sizeof(char));
*(line + (i-1)) = '\0';
*(line + (i-2)) = c;
}
free(temp);
if( i == 1) return NULL;
return line;
}
main() {
int lasttime = 0, timestamp, duration, tokens;
char * userID = NULL;
char * lastuserID = NULL;
char * line = NULL;
float weight,lastweight,change,changePerTime;
head = new_node(0,"",0.0);
last = head;
FILE *fp = fopen("C:\\Users\\chris\\Desktop\\School\\York\\cse\\2031 Software Tools\\Labs\\6\\input.txt","r");
while( (line = read_line(fp)) != '\0') {
printf("%s\n",line);
//free(userID);
line = strtok(line, " \n");
if (line == NULL || sscanf(line,"%d",×tamp) < 1 || timestamp == 0){
printf("%s\n","Invalid time");
continue;
}
line = strtok(NULL, " \n");
if(line == NULL || isdigit(line[0]) || line[0] == '.') {
printf("Illegal userID");
//free(line);
continue;
}
userID = (char * )malloc( (strlen(line)+1) * sizeof(char));
strcpy(userID,line);
strcat(userID," ");
do{
line = strtok(NULL," \n");
if(line != NULL && !isdigit(line[0]) && line[0] != '.'){
strcat(userID,line ); // adds ' ' and '\0'
strcat(userID," ");
}
}while(line != NULL && line[0] != '.' && !isdigit(line[0]) );
userID[strlen(userID)-1] = '\0'; //erases the tailing space.
if(strlen(userID) > 179){
printf("Illegal userID\n");
printf("mid");
continue;
printf("%s\n","after" );
}
if(line != NULL)
tokens = sscanf(line,"%f", &weight);
if(line == NULL || tokens < 1 || weight < 30.0 || weight > 300.0)
{printf("Illegal weight\n"); continue; }
if (lasttime >= timestamp){
printf("Nonmonotonic timestamps\n");
continue;
}
lasttime = timestamp;
// record is valid apst this point.
/* t = last occurence of this userID, p = last userID*/
for(p = head, t = NULL; p != NULL; p = p->next)
{
if(strcmp(userID,p->id) == 0)
t=p;
last = p; // set last to last p.
}
if(t == NULL)
printf("OK newuser\n");
else if(t != NULL)
{
duration = timestamp - t->time;
change = weight - t->weight;
changePerTime = change / duration;
if(changePerTime < -MAX_CHANGE || changePerTime > MAX_CHANGE)
printf("Suspiciously large weight change\n");
else
printf("OK\n");
}
/* add new node to end of list */
last->next = new_node(timestamp,userID,weight);
/* update lastnode */
last = last->next;
free(line);
}
fclose(fp);
/* count sum of id's for last valid user*/
int count=0;
for(p = head->next; p !=NULL; p=p->next)
{
if(strcmp(last->id,p->id) == 0)
count++;
}
//fclose(f); // use if input from file is uncommented
// adds 1 to both demensions to hole axis
int tHeight = 11;
int tWidth = count + 1;
int qHeight = 10;
int qWidth= count;
/* builds the barchart */
char bc[tHeight][tWidth]; // + 1 for y-axis
/* draws axis and orgin */
int a,b;
for(a=0; a<tHeight; a++)
{
for(b=0;b<tWidth; b++)
{
if(a == qHeight && b == 0)
bc[a][b] = '+';
else if(a < tHeight && b == 0)
bc[a][b] = '|';
else if(a == qHeight && b > 0)
bc[a][b] = '-';
}
}
/* prints the bars */
int j=1, i, k, bh;
for(p = head; p != NULL, j < tWidth; p=p->next)
{
if(strcmp(last->id,p->id) == 0)
{
for(i = 9, k=0, bh = (int)(p->weight / 30);i >= 0; i--)
{
if(k < bh)
{
bc[i][j] = '*';
k++; // barheight
}
else
bc[i][j] = ' ';
}
j++;
}
}
/* prints the barchart */
int m, n;
for(m=0; m < tHeight; m++)
{
for(n=0; n < tWidth; n++)
{
printf("%c",bc[m][n]);
}
printf("%c",'\n');
}
}
答案 0 :(得分：1)
malloc次呼叫未导致分段错误。但是你以后可以使用它们。
一些注意事项
您的printf("read line")语句在调用时不会立即打印出来，因为输出是缓冲的。如果您希望立即打印，请执行printf("read line\n")。然后，您将看到执行和使用您分配的微小缓冲区的代码都会导致崩溃。
在while循环中，您正在执行更多malloc次调用，并将返回值分配给变量，例如temp和line，而不释放先前的内存temp和line持有的指针，从而导致一些内存泄漏。您评论的realloc是更好的思考过程：line = realloc(line, ++i * sizeof(*line));。同样适用于temp。
<小时/> 内存分配问题
这里有一个非常棘手的问题：
userID = (char * )malloc( (strlen(line)+1) * sizeof(char));
strcpy(userID,line);
strcat(userID," ");
userID可以保持line（strlen(line)）中字符串的长度加上一个字节。但是null终结符需要多一个字节。您的strcat(userID, " ")将超出分配缓冲区的长度userID一个字节。
答案 1 :(得分：0)
我解决了这个问题！问题根本不是read_line函数，而是userID字符串的内存分配。将用户的malloc（）移动到循环的开头可以解决问题。
为该行的userID部分分配的内存量基于整行的长度。例如：malloc（strlen（line）+2）。然而，这是在线上调用strtok（）几次之后完成的，这将分配比整行长度短的内存块。这是因为strtok（）在行中指定分隔符的每个实例处放置了空终止符'\ 0'，而strlen（）只计算从传递的字符指针到它遇到的第一个'\ 0'的长度。
无论如何，谢谢你的帮助！
-Chris
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#define DELIM " " /* the delimiter */
#define MAX_CHANGE (10.0/86400.0) /* 10kg/day */
/* seconds in a day is 24 hours * 60 minutes * 60 seconds */
/* Defines Node structure. */
struct Node{
char *id;
float weight;
int time;
struct Node *next;
} *head, *p, *t, *last;
/* Constructor which returns a pointer to a new node. */
struct Node * new_node(int time, char *id, float w)
{ /*note malloc returns a pointer */
struct Node *node = (struct Node *)malloc(sizeof(struct Node));
node->time = time;
node->id = malloc(strlen(id) + 1);
strcpy(node->id, id); //duplicate the id, so new node has own copy.
node->weight = w;
node->next = NULL;
return node;
}
/* reads in line of characters until either a EOF or '\n' is encountered
then places a the terminator '\0' at the end */
char * read_line(FILE *in)
{
int i = 1;
char * s = NULL;
char c;
do{
s = realloc(s,i); //strlen does not work on NULL strings
if(s == NULL || s == "")
{
printf("%s\n","out of memory");
exit(1);
}
*(s + (i-1)) = '\0'; // ensures null terminated
if(i > 1)
*(s + (i-2)) = c;
i++;
}
while( (c = getc(in)) != EOF && c != '\n' );
if (c == '\n')
return s;
else if(c == EOF)
return NULL;
}
main() {
int lasttime = 0, timestamp, duration, tokens;
char * userID = NULL;
char * lastuserID = NULL;
char * line = NULL;
float weight,lastweight,change,changePerTime;
head = new_node(0,"",0.0);
last = head;
FILE *fp = fopen("C:\\Users\\chris\\Desktop\\School\\York\\cse\\2031 Software Tools\\Labs\\6\\tests\\04.in","r");
while((line = read_line(fp)) != NULL) {
userID = malloc(strlen(line)+2); // max userID length is line length**
line = strtok(line, " \n");
if (line == NULL || sscanf(line,"%d",×tamp) < 1 || timestamp == 0){
printf("%s\n","Invalid time");
continue;
}
line = strtok(NULL, " \n");
if(line == NULL || isdigit(line[0]) || line[0] == '.') {
printf("%s\n","Illegal userID");
//free(line);
continue;
}
strcpy(userID,line);
strcat(userID," ");
do{
line = strtok(NULL," \n");
if(line != NULL && !isdigit(line[0]) && line[0] != '.'){
strcat(userID,line ); // adds ' ' and '\0'
strcat(userID," ");
}
}while(line != NULL && line[0] != '.' && !isdigit(line[0]) );
userID[strlen(userID)-1] = '\0'; //erases the tailing space.
if(strlen(userID) > 179){
printf("Illegal userID\n");
free(userID);
free(line);
continue;
}
if(line != NULL)
tokens = sscanf(line,"%f", &weight);
if(line == NULL || tokens < 1 || weight < 30.0 || weight > 300.0)
{printf("Illegal weight\n"); continue; }
if (lasttime >= timestamp){
printf("Nonmonotonic timestamps\n");
continue;
}
lasttime = timestamp;
// record is valid apst this point.
/* t = last occurence of this userID, p = last userID*/
for(p = head, t = NULL; p != NULL; p = p->next)
{
if(strcmp(userID,p->id) == 0)
t=p;
last = p; // set last to last p.
}
if(t == NULL)
printf("OK newuser\n");
else if(t != NULL)
{
duration = timestamp - t->time;
change = weight - t->weight;
changePerTime = change / duration;
if(changePerTime < -MAX_CHANGE || changePerTime > MAX_CHANGE)
printf("Suspiciously large weight change\n");
else
printf("OK\n");
}
/* add new node to end of list */
last->next = new_node(timestamp,userID,weight);
/* update lastnode */
last = last->next;
free(line);
} // end of input loop
fclose(fp);
/* count sum of id's for last valid user*/
int count=0;
for(p = head->next; p !=NULL; p=p->next)
{
if(strcmp(last->id,p->id) == 0)
count++;
}
//fclose(f); // use if input from file is uncommented
// adds 1 to both demensions to hole axis
int tHeight = 11;
int tWidth = count + 1;
int qHeight = 10;
int qWidth= count;
/* builds the barchart */
char bc[tHeight][tWidth]; // + 1 for y-axis
/* draws axis and orgin */
int a,b;
for(a=0; a<tHeight; a++)
{
for(b=0;b<tWidth; b++)
{
if(a == qHeight && b == 0)
bc[a][b] = '+';
else if(a < tHeight && b == 0)
bc[a][b] = '|';
else if(a == qHeight && b > 0)
bc[a][b] = '-';
}
}
/* prints the bars */
int j=1, i, k, bh;
for(p = head; p != NULL, j < tWidth; p=p->next)
{
if(strcmp(last->id,p->id) == 0)
{
for(i = 9, k=0, bh = (int)(p->weight / 30);i >= 0; i--)
{
if(k < bh)
{
bc[i][j] = '*';
k++; // barheight
}
else
bc[i][j] = ' ';
}
j++;
}
}
/* prints the barchart */
int m, n;
for(m=0; m < tHeight; m++)
{
for(n=0; n < tWidth; n++)
{
printf("%c",bc[m][n]);
}
printf("%c",'\n');
}
}