Passing Arguments

This is a discussion on Passing Arguments within the C Programming forums, part of the General Programming Boards category; I am working on a linked list using separate files. I have a working linked list where all my functions ...

  1. #1
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    Question Passing Arguments

    I am working on a linked list using separate files. I have a working linked list where all my functions are in one file but when I try to compile using separate files I have issues. I don't understand what changed with the pointers. Or am I not including things correctly, also prior to separate files I didn't use a header file or function prototypes, but I believe I have those correct.


    prog4.c: In function ‚main‚:
    prog4.c:37: warning: passing argument 1 of ‚insert‚ from incompatible pointer type
    prog4.c:37: warning: passing argument 2 of ‚insert‚ from incompatible pointer type
    prog4.c:37: warning: passing argument 3 of ‚insert‚ makes integer from pointer without a cast
    prog4.c:64: error: request for member ‚next‚ in something not a structure or union
    prog4.c:75: warning: passing argument 1 of ‚remnode‚ from incompatible pointer type


    Code:
    header.h
    
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    
    struct node {
    
            char string[21];
            int num;
            struct node *next;
    
    };
    
    void insert(struct node *, struct node *, int, char *);
    
    void remnode(struct node *);

    Code:
     
    
    #include "header.h"
    
    int main(int argc, char *argv[])
    {
    
            FILE *infile, *outfile;         /*Creates an infile, and
                                            outfile*/
    
            struct node *head;
    
            struct node *current;           /*Creates a head and current
                                            node*/
    
            head = current = NULL;          /*Set the head and current node
                                            to NULL*/
    
            infile = fopen("prog4.in","r"); /*opens infile for reading*/
    
            outfile = fopen("prog4.out","w");/*opens outfile for writing*/
    
            int num;                        /*variable to hold the integer
                                            value read in by fscanf */
    
            char buffer[21];                /*array to hold the characters
                                            read in by fscanf */
    
            while(fscanf(infile, "%d %s", &num, buffer) == 2){
    
                                            /*while the fscanf function retur$
                                            which occurs when it reads in and
                                            integer and the string, do the
                                            following */
    
               insert(&head, &current, &num, buffer);
    
                          struct node *printnode = head;
    
                                            /*create a temporary node for
                                            printing to a file*/
    
                    while(printnode != NULL){
    
                                            /*while printnode exists, or
                                            while another node exists in the
                                            list, do the following*/
    
                            fprintf(outfile, "%s %d\n",
                            (*printnode).string, (*printnode).num);
    
                                            /*print to the outfile the
                                            number and the string from the
                                            current print node*/
    
                            fprintf(outfile, "\n");
    
                            printnode=printnode.next;
    
                                            /*set printnode to be the next no$
    
                    }/*while(printnode != NULL){...*/
    
            } /*while(fscanf(infile, "%d %s", &num, buffer) == 2){...*/
    
            while(head != NULL){
    
    
                    remnode(&head);
    
            }/*while(head != NULL){...*/
    
            fclose(infile);
            fclose(outfile);
    
                 return 0;
    
    } /*end main*/
    Code:
    
    /*insert.c*/
    
    void insert(struct node **front, struct node **current, int num,
    char *buffer[]){
    
            struct node *new = (struct node*)malloc(sizeof(struct node));
    
                            /*creates a node and allocates memory - 1030*/
    
            if(new != NULL) /*checks to makes sure memory is allocated - 1*/
            {
    
                    (*new).string = buffer;
                    (*new).num = num;
    
                    if(*front == NULL)      /*if the front node does not
                                            exist set it equal to new - 1*/
                    {
    
                            *front = new;
                            (*new).next = NULL;
    
                    } /*end if*/
    
    
                    if (strcmp(new.string, *current.string) == 0){
    
                                            /*if new.string is equal to
                                            current.string insert new after
                                            current*/
    
                            (*new).next = NULL;
                            (**front).next = new;
    
                    }/*if (strcmp(new.string, *current.string) == 0){*/
    
                    if (strcmp(new.string, *front.string) < 0){
    
      int i;
    
                    if (strcmp(new.string, *front.string) > 0){
    
                                            /*if new.string comes after
                                            front.string check the next node
                                            by calling insert and passing
                                            front.next into front*/
    
                            insert(&front.next, &current, &num, buffer);
    
    
    
                    }/*if (strcmp(new.string, *current.string) > 0){*/
    
    
    
    
                    *current = new;         /*set the current node to new
                                            - 2*/
    
    
            } /*if(new != NULL){...*/
    
    } /*end insert*/
    Code:
    /*remnode.c*/
    void remnode(struct node **front)
    
                            /*function to remove a node*/
    {
    
            if(front != NULL) /*checks to make sure list is not empty*/
            {
    
                    struct node *temp;      /*create a temporary node*/
    
                    temp = NULL;            /*set the temporary node to
                                            null*/
    
                    temp = *front;          /*set the temp to the front
                                            node*/
    
                    *front = *front.next;
                                            /*set the front node to the
                                            next node*/
    
                    free((*temp).string);   /*free the memory for the string
                                            from the previous front node*/
    
                    free((*temp).num);      /*free the memory for the num
                                            from the previous front node*/
    
                    free(temp);             /*free the memory for previous
                                            front node*/
    
            } /*end if*/
    
    } /*end remnode*/
    Last edited by bolivartech; 10-14-2009 at 10:15 PM.

  2. #2
    ATH0 quzah's Avatar
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    You are passing the address of a pointer, and your function wants a pointer.


    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    > header.h
    > void insert(struct node *, struct node *, int, char *);


    >void insert(struct node **front, struct node **current, int num,
    >char *buffer[]){

    To quote Early: Does that seem right to you?

  4. #4
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    I completely understand what you are saying. I guess I didn't quite get my function prototypes right. I had to correct those errors before in my original program, and I figured it out on my own then, I'm not sure why the prototypes and the header file are throwing me off. Below is the error I get after the changes. I'm not sure I've ever seen errors like that, how do I know what line the error is on? Thanks!

    /tmp/ccko1umN.o: In function `main':
    prog4.c.text+0x66): undefined reference to `insert'
    prog4.c.text+0xda): undefined reference to `remnode'
    collect2: ld returned 1 exit status

  5. #5
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    Looks like you left off the .o that has the insert and remnode in it. Those are Linker errors, not compiler errors.

    >collect2: ld returned 1 exit status

    LD is your dynamic linker.

  6. #6
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    Thanks for the assistance, I included the header file into my other .c files and compiled it as gcc *.c This let me clear up the rest of my errors. I have a segmentation fault now, but I think I can browse through my code and find where I made a mistake. But if anyone sees something above that might lead to that let me know. Thanks again!

  7. #7
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    An easy way to debug is to put this on (almost) every other line:

    printf("%s:%i\n", __FUNCTION__, __LINE__);

    This works for gcc, but I don't know about other compilers.

  8. #8
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    Basically put in a print to see where the program get hung up at?

  9. #9
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by bolivartech
    Basically put in a print to see where the program get hung up at?
    Yes, but you might want to consider using a debugger instead, or at least make those print statements conditional based on some flag variable (or macro).
    C + C++ Compiler: MinGW port of GCC
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  10. #10
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    Well the printf to check my program has worked out well. I was moving right along finding my errors when it through this at me after another compile. I need to make some changes to my input file to make sure all of my insert function works but since this is an error about free(), at least I think. Then it is dealing with my remnode function. What is it trying to tell me?

    Code:
    in main after insert
    *** glibc detected *** ./a.out: free(): invalid pointer: 0x0000000000601538 ***
    ======= Backtrace: =========
    /lib/libc.so.6[0x2b4a2c4ffb23]
    /lib/libc.so.6(cfree+0x8c)[0x2b4a2c50326c]
    ./a.out[0x400ae2]
    ./a.out[0x400a5e]
    /lib/libc.so.6(__libc_start_main+0xf4)[0x2b4a2c4ad8e4]
    ./a.out[0x400729]
    ======= Memory map: ========
    00400000-00401000 r-xp 00000000 00:16 134221046                          /nas/lkemp/CIS3333/prog4/a.out
    00600000-00601000 rw-p 00000000 00:16 134221046                          /nas/lkemp/CIS3333/prog4/a.out
    00601000-00622000 rw-p 00601000 00:00 0                                  [heap]
    2b4a2c273000-2b4a2c28f000 r-xp 00000000 08:01 32787                      /lib/ld-2.5.so
    2b4a2c28f000-2b4a2c2a3000 rw-p 2b4a2c28f000 00:00 0
    2b4a2c48e000-2b4a2c490000 rw-p 0001b000 08:01 32787                      /lib/ld-2.5.so
    2b4a2c490000-2b4a2c5d7000 r-xp 00000000 08:01 32805                      /lib/libc-2.5.so
    2b4a2c5d7000-2b4a2c7d7000 ---p 00147000 08:01 32805                      /lib/libc-2.5.so
    2b4a2c7d7000-2b4a2c7da000 r--p 00147000 08:01 32805                      /lib/libc-2.5.so
    2b4a2c7da000-2b4a2c7dc000 rw-p 0014a000 08:01 32805                      /lib/libc-2.5.so
    2b4a2c7dc000-2b4a2c7e2000 rw-p 2b4a2c7dc000 00:00 0
    2b4a2c7e2000-2b4a2c7ef000 r-xp 00000000 08:01 32830                      /lib/libgcc_s.so.1
    2b4a2c7ef000-2b4a2c9ef000 ---p 0000d000 08:01 32830                      /lib/libgcc_s.so.1
    2b4a2c9ef000-2b4a2c9f0000 rw-p 0000d000 08:01 32830                      /lib/libgcc_s.so.1
    2b4a30000000-2b4a30021000 rw-p 2b4a30000000 00:00 0
    2b4a30021000-2b4a34000000 ---p 2b4a30021000 00:00 0
    7fff7e821000-7fff7e837000 rw-p 7fff7e821000 00:00 0                      [stack]
    ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vdso]
    Aborted (core dumped)

    Code:
    *remnode.c*/
    
    #include "prog4.h"
    
    void remnode(struct node **front)
    
                            /*function to remove a node*/
    {
    
            if(front != NULL) /*checks to make sure list is not empty*/
            {
    
                    struct node *temp;      /*create a temporary node*/
    
                    temp = NULL;            /*set the temporary node to
                                            null*/
    
                    temp = *front;          /*set the temp to the front
                                            node*/
    
                    *front = (**front).next;
                                            /*set the front node to the
                                            next node*/
    
                    free((*temp).string);   /*free the memory for the string
                                            from the previous front node*/
    
                    free(&(*temp).num);             /*free the memory for the num
                                            from the previous front node*/
    
                    free(temp);             /*free the memory for previous
                                            front node*/
    
            } /*end if*/
    
    } /*end remnode*/

  11. #11
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    By the way something I did to get it to compile was change the free(*temp).num; line to include the &. with out it I get:

    remnode.c: In function ‚remnode‚:
    remnode.c:28: warning: passing argument 1 of ‚free‚ makes pointer from integer without a cast

  12. #12
    and the Hat of Guessing tabstop's Avatar
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    Code:
    free(&(*temp).num);
    Did num come from malloc? (Looking at this, I doubt it, but you never know.) If you didn't malloc it, don't free it.

  13. #13
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    Doesn't make any sense to free() each member of struct node when you're malloc()'ing memory for the struct as a whole, as in
    Code:
    /* these two free() calls don't make sense */
    free((*temp).string);
    free(&(*temp).num);
    
    /* just free() struct node which comes a couple of code statements later */
    free(temp);
    Last edited by itCbitC; 10-15-2009 at 02:36 PM.

  14. #14
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    Quote Originally Posted by laserlight View Post
    Yes, but you might want to consider using a debugger instead, or at least make those print statements conditional based on some flag variable (or macro).
    One cannot always use a debugger, but almost always can one use print statements (the exception to this, of course, would be bit code for PICs etc).

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