Assigning a char in a C struct

Question

Essentially I am having a very basic problem... A little new at C. I'm making a node structure that stores a name (string) and its type (char, either 'D' or 'F'). The string works fine, the char doesn't seem to.

#include <stdlib.h>
#include <stdio.h>
#include <string.h>


char line[128];
char command[16], pathname[64];
char dirname[64], basename[64];

typedef struct {
  char name[64];
  char type;
  struct NODE *childPtr, *siblingPtr, *parentPtr;
} NODE;

NODE *root, *cwd;

initialize(){
  root = malloc(sizeof(NODE));
  strcpy(root->name, "/");
  root->type = 'D';
}  

main()
{
  while(1){
    printf("Input a command: ");
    gets(line);
    printf("Command inputed -> %s\n", line);
    printf("Root's name -> %s\n", root->name);
    printf("Root's type -> %c\n", root->type);
  }
}

Now when I do this, it prints out the name just fine, but Segmentation Faults on the line that should print the type. I also tried defining type with "root.type = 'D';" as well.

EDIT: Copy pasted exact code now. Some things have no use since I am just testing the first part of it, still a work in progress.

Hint: if using `malloc(sizeof(*root))` you never have to care if the type of the variable is really the same you allocate. — too honest for this site, Sep 17 '15 at 22:26
if this was really a syntax problem i doubt this would have come as far as a segmentation fault ... — Fantastic Mr Fox, Sep 17 '15 at 22:30
Valid signature for main is at least `int main(void)`. The one likely required by your environment is `int main(int argc, char *argv[])` — too honest for this site, Sep 17 '15 at 22:35
**Do not use `gets`!**. This is an invitation to _undefined behaviour_. Use `fgets` on `stdin` instead. — too honest for this site, Sep 17 '15 at 22:37
Also, either use a more modern compiler or use a more modern C standard (or both). Functions in C have required return types for 16 years now... — dreamlax, Sep 17 '15 at 22:38
@bock-steve Is that really your exact code? Where do you call `initialize`? — kaylum, Sep 17 '15 at 22:38
Um.... @AlanAu.... I'm gonna go wallow in my own shame now. You hit the nail on the head right there. I'm sorry for wasting everyone's time and thank you for the help! — bock.steve, Sep 17 '15 at 22:45
Happens to the best of us. Probably should just delete this question as it will not be useful to anyone else going forward. And don't we all wish there was always such an easy way to erase embarrassing moments from the Internet :-) — kaylum, Sep 17 '15 at 22:49
Yup, flagged it for deletion (wont let me delete due to answers) — bock.steve, Sep 17 '15 at 22:54
when calling malloc(), always check (!=NULL) the returned value to assure the operation was successful — user3629249, Sep 19 '15 at 07:09
regarding this line: `struct NODE *childPtr, *siblingPtr, *parentPtr;` It would be much better to include a 'tag' name in the struct definition, then use the 'tag' name as in: `struct tagNode *childPtr, *siblingPtr, *parentPtr;` Suggest only one field/variable per statement for clarity and ease of documentation. — user3629249, Sep 19 '15 at 07:16

LearningCODE · Answer 1 · 2015-09-17T23:00:23.157

1

You have an error when declaring your struct... You misspelled struct as 'strcut'.

You also need to do

root = malloc(sizeof(*root));
...
free(root);//should be the last line
return 0;

EDIT: DON'T USE gets() ever, it is almost certain that you will run into problems...

EDIT 2 : function initialize() should be given return type void. Then you have to call the function in main. Should look like this.

#include <stdlib.h>
#include <stdio.h>
#include <string.h>


char line[128];
char command[16], pathname[64];
char dirname[64], basename[64];

typedef struct {
  char name[64];
  char type;
  struct NODE *childPtr, *siblingPtr, *parentPtr;
} NODE;

NODE *root, *cwd;

void initialize(){
  root = malloc(sizeof(*root));
  strcpy(root->name, "/");
  root->type = 'D';
}

main()
{
    initialize();
  while(1){
    printf("Input a command: ");
    fgets(line,128, stdin);
    printf("Command inputed -> %s\n", line);
    printf("Root's name -> %s\n", root->name);
    printf("Root's type -> %c\n", root->type);
    if (line[0] == 'q' && strlen(line)==2)break;//added so I can break loop....
  }
  free(root);
}

edited Sep 17 '15 at 23:00

answered Sep 17 '15 at 22:30

LearningCODE

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That doesn't answer the actual question. Put it as a comment by all means but not an answer. – kaylum Sep 17 '15 at 22:34
@AlanAu I cannot comment... i would have but I do not have the reputation yet... thanks for the downvote – LearningCODE Sep 17 '15 at 22:41
Upvote for `gets()`. and for stating that all memory should be freed at some point. It may not answer the question, but it is useful information nonetheless. – dreamlax Sep 17 '15 at 22:44
I didn't downvote. But the rules are there for a reason. If you haven't got enough rep for comments then the correct response is not to work around the rules by posting non-answers as answers. The correct response is to get more rep points and not comment until you do. – kaylum Sep 17 '15 at 22:45
actually, the inclusion of the call to `initialize()` is the answer to the problem – user3629249 Sep 19 '15 at 07:18

kyle k · Answer 2 · 2015-09-17T22:32:30.787

-1

you where missing some header files and you misspelled struct, you should also free the allocated memory for the structure.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    char name[64];
    char type;
} NODE;

NODE *root;

int main()
{
    root = malloc(sizeof(NODE));
    strcpy(root->name, "test");
    root->type = 'D';
    printf("Name = %s\n", root->name);
    printf("Type = %c\n", root->type);
    free(root);
    return 0;
}

edited Sep 17 '15 at 22:32

answered Sep 17 '15 at 22:28

kyle k

5,134
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I didn't include the headers when i typed this up (didn't copy paste, on seperate comp), and struct is correctly spelled in the code, was just a typo here. – bock.steve Sep 17 '15 at 22:30
All valid problems you have identified. But how do any of those cause a seg fault? – kaylum Sep 17 '15 at 22:31

CIsForCookies · Answer 3 · 2015-09-17T22:39:17.987

-3

typedef strcut should be struct --> that should be a compilation error

and that should do it

edited Sep 17 '15 at 22:39

answered Sep 17 '15 at 22:29

CIsForCookies

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No to 2, read this: http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc – Fantastic Mr Fox Sep 17 '15 at 22:30
@Ben That is very strange. That was what I learned at the university. Also the compiler gives me an error for not casting, though I included stdlib, care to explain? – CIsForCookies Sep 17 '15 at 22:32
1

@CIsForCookies `C` does not require `malloc` result to be cast. But `C++` does. – kaylum Sep 17 '15 at 22:35
Was about to rewrite that. I compiled it on g++ instead of gcc and thought it wouldn't matter. thx. BTH, can you explain why C++ require but C doesn't? – CIsForCookies Sep 17 '15 at 22:38
1

@ClsForCookies It is simply a fundamental difference between C and C++. In C, implicit conversion from pointer to void to another pointer type is allowed, but C++ introduces a lot of ways to increase type safety, there is little need to store things in `void*` when compared to C. – dreamlax Sep 17 '15 at 22:41

Assigning a char in a C struct

3 Answers3