>我有一个基本程序，它通过readline函数从用户那里获取用户命令"命令varname =变量"。然后，它分析字符串以将每个部分存储到字符串变量中。 我遇到的问题是我收到一个错误：分段默认值（核心转储），这应该来自非法内存访问，但是我已经在示例输入上逐行浏览了我的程序："设置射线"，我无法弄清楚这是在哪里发生的。 我的预期结果是命令应该包含 set，Varname 应该包含射线，值应该为 NULL 这是显示错误的代码以及示例输入和输出。 我还看到了一个错误：总线（核心转储）出现一次。 任何想法这个错误来自哪里？
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <readline/readline.h>
#include <readline/history.h>
/* Simple example of using gnu readline to get lines of input from a user.
Needs to be linked with -lreadline -lcurses
add_history tells the readline library to add the line to it's
internal histiry, so that using up-arrow (or ^p) will allows the user
to see/edit previous lines.
*/
int main(int argc, char **argv) {
char * s;
char * Command;
char * Varname;
char * Value;
while (s=readline("Enter Name: ")) {
add_history(s); /* adds the line to the readline history buffer */
printf("Hello %sn",s);/*output message to the user*/
int part = 1;
int i;
for (i = 0; i < strlen(s); i++)
{
while((isspace(s[i]) || s[i] == '=') && (i < strlen(s)))
{
i++;//parse the string for the next portion of the command
}
if(i >= strlen(s))
{
printf("Error: Command not properly formatted!n");
break;//terminate the for loop
}
if(part == 1)//grab the command
{
int size1 = 0;//size of the command
int j = i;//index of the first non-space character in this portion of the string
while(!isspace(s[j]))//determine the size of the command, j will point to space when the loop exits
{
size1++;
j++;
}
Command = (char*) malloc (size1+1);//allocate space to hold the characters of the command along with the terminating ' ' character
int d = 0;//destination index
while(i<j)
{
Command[d] = s[i];//copy the characters of the command portion of s over to the command array
d++;
i++;
}
Command[d] = ' ';//terminating null character
part++;//increment the part of the command
}
else if(part == 2)//grab the varname
{
int size2 = 0;//initialize the size of the character array which will hold the variable name
int k = i;
while(!isspace(s[k]))//determine the size of the varname, k will be at the next space when the loop exits
{
size2++;
k++;
}
Varname = (char*) malloc (size2+1);//allocate space to hold the characters of the Varname along with the terminating ' ' character
int e = 0;
while(i<k)
{
Varname[e] = s[i];//copy the characters of the Varname portion of s over to the Varname string
e++;
i++;
}
Varname[e] = ' ';
part++;//increment part
}
else if(part == 3)//grab the value if one is given
{
int size3 = 0;//initialize the size of the character array which will hold the value of the environment variable
int l = i;
while(!isspace(s[l]) && s[l] != ' ')//determine the size of the varname and check if we've reached the end of the string
{
size3++;
l++;
}
Value = (char*) malloc (size3+1);//allocate space to hold the characters of the Value along with the terminating ' ' character
int f = 0;
while(i<l)
{
Value[f] = s[i];//copy the characters of the command portion of s over to the command array
f++;
i++;
}
Value[f] = ' ';
}
}
/*print out the sections of the full command*/
if(Command != NULL)
{
printf("Hey %sn",Command);
}
if(Varname != NULL)
{
printf("Hey %sn",Varname);
}
if(Value != NULL)
{
printf("Hey %sn",Value);
}
/* clean up! */
free(s);
free(Command);
free(Varname);
free(Value);
}
return(0);
}
示例输入/输出：
Enter Name: set ray = 21
Hello set ray = 21
Hey set
Hey ray
Hey 21
Enter Name: print ray
Hello print ray
Hey print
Hey ray
Hey
Enter Name: delete varname
Hello delete varname
Hey delete
Hey varname
Hey delete
Enter Name: print raymond
Hello print raymond
Hey print
Hey raymond
Hey
Enter Name: delete variable
Hello delete variable
Hey delete
Hey variable
Segmentation fault (core dumped)
声明三个指针而不初始化它们
char * Command;
char * Varname;
char * Value;
根据用户输入的内容，这些内容可能不会全部初始化为指向for循环中动态分配的内存。 如果它们没有全部初始化，稍后尝试free它们可能会崩溃
free(Command);
free(Varname);
free(Value);
最简单的解决方法是在开始处理每行时初始化要NULL的所有变量
while (s=readline("Enter Name: ")) {
Command = NULL;
Varname = NULL;
Value = NULL;
然后可以安全地呼叫free，即使它们仍设置为NULL。