malloc链表时出现分段错误

Question

I've created two structs:

typedef struct Student{
    int id; 
    char* name;
    int birthYear;
    int finishedCourses;
    int courseCredits;
    double avarage;
    int coursesNow;
    NodeCourses* courses;

}Student;

typedef struct NodeS{
    Student student;
    struct NodeS* next;
}NodeS;

So I can now create a linked list of students.

one of the things I want to do is to ask the user to put details about each student.

so Ive created a function that called "addNewStudent"

first in the function it does this:

NodeS* newStudent;
    newStudent=(NodeS*)malloc(sizeof(NodeS));

and than, when I am asking the user to insert a name I put it in a string called "name" and I want to malloc again the name string. so I do this:

newStudent->student.name=(char*)malloc(sizeof(char)*strlen(name));

and that line gives me segmentation fault.

ps: Ive checked the string is in the write size and that i get is correctly.

what should I do?

Answer 1

 newStudent->student.name=(char*)malloc(sizeof(char)*strlen(name));

I am taking you at your word that this exact line of code causes a segmentation fault. There are three things this line of code does, any one of which could be your cause:

1) You do strlen(name) . If name does not point to a valid C-style string with a proper nul terminating byte, this could segfault. You can test this theory by adding this before the line of code:

printf("About to call strlen\n");
printf("Got: %d\n", strlen(name));

If this is the problem, you will see the first line of output but not the second since the segfault will terminate the program before it gets a chance to execute.

2) You call malloc . It's possible that the heap has become corrupt due to a previous double free, use after free, buffer overrun, or similar problem. So the call to malloc may be the victim of previous damage. You can test this by adding this code:

printf("About to call strlen\n");
printf("Got: %d\n", strlen(name));
printf("About to call malloc\n");
char *o = malloc(sizeof(char) * strlen(name));
printf("Malloc didn't segfault\n");
newStudent->student.name=o;

3) You assign to newStudent->student.name . If, for example, newStudent is NULL or otherwise doesn't point to valid contents, that could be your issue. You can test this by adding this code:

printf("About to call strlen\n");
printf("Got: %d\n", strlen(name));
printf("About to call malloc\n");
char *o = malloc(sizeof(char) * strlen(name));
printf("Malloc didn't segfault\n");
printf("Trying to access newStudent->student.name\n");
printf("newStudent->student.name=%p\n", newStudent->student.name);
newStudent->student.name=o;
printf("Actually, the whole statement worked\n");

If you see all the printf s but your program still crashes, then you were wrong about the statement causing the segfault.