Whats wrong with following Linked List insertion? (I just put one insertion function call to test) | Together C & C++ | Page 1

pastel finch Jul 19, 2024, 12:07 AM

#

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

typedef struct Song {
    char name[25];
    int duration;
    struct Song* next_alpha;
} Song;
typedef Song* SongPtr;

typedef struct SongList {
    int size;
    SongPtr head_alpha;
} SongList;
typedef SongList* SongListPtr;

void insert(SongListPtr*, char[], int);

int main() {
    SongList songs;
    SongListPtr songsPtr = &songs;
    songsPtr->size = 0;
    songsPtr->head_alpha = NULL;
    insert(&songsPtr, "HelloWorld", 150);
    printf("End\n");
    return 0;
}

void insert(SongListPtr* songsPtr, char name[], int duration) {
    SongPtr newSongPtr = (SongPtr)malloc(sizeof(Song));
    if(newSongPtr != NULL) {
        strncpy(newSongPtr->name, name, 24);
        newSongPtr->duration = duration;
        (*songsPtr)->size += 1;

        SongPtr previousPtr = NULL;
        SongPtr currentPtr = (*songsPtr)->head_alpha;
        while(currentPtr->next_alpha != NULL  &&  strcmp(newSongPtr->name, currentPtr->next_alpha->name) > 0) {
            previousPtr = currentPtr;
            currentPtr = currentPtr->next_alpha;
        }

        if(previousPtr == NULL) {
            newSongPtr->next_alpha = (*songsPtr)->head_alpha;
            (*songsPtr)->head_alpha = newSongPtr;
        }
        else {
            previousPtr->next_alpha = newSongPtr;
            newSongPtr->next_alpha = currentPtr;
        } 
        printf("done\n");
        
    }
    else { 
        printf("Memory can not allocated.");
    }
}```

oblique anvilBOT Jul 19, 2024, 12:07 AM

#

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plush wren Jul 19, 2024, 12:19 AM

#

What's happening that shouldn't be?

hazy jackal Jul 19, 2024, 12:58 AM

#

You don't check if currentPtr is NULL.
If the list is empty, so (*songsPtr)->head_alpha is NULL, then so is currentPtr.

#

;compile

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

typedef struct Song {
    char name[25];
    int duration;
    struct Song* next_alpha;
} Song;
typedef Song* SongPtr;

typedef struct SongList {
    int size;
    SongPtr head_alpha;
} SongList;
typedef SongList* SongListPtr;

void insert(SongListPtr*, char[], int);

int main() {
    SongList songs;
    SongListPtr songsPtr = &songs;
    songsPtr->size = 0;
    songsPtr->head_alpha = NULL;
    insert(&songsPtr, "HelloWorld", 150);
    printf("End\n");
    return 0;
}

void insert(SongListPtr* songsPtr, char name[], int duration) {
    SongPtr newSongPtr = (SongPtr)malloc(sizeof(Song));
    if(newSongPtr != NULL) {
        strncpy(newSongPtr->name, name, 24);
        newSongPtr->duration = duration;
        (*songsPtr)->size += 1;

        SongPtr previousPtr = NULL;
        SongPtr currentPtr = (*songsPtr)->head_alpha;
        while(currentPtr->next_alpha != NULL  &&  strcmp(newSongPtr->name, currentPtr->next_alpha->name) > 0) {
            previousPtr = currentPtr;
            currentPtr = currentPtr->next_alpha;
        }

        if(previousPtr == NULL) {
            newSongPtr->next_alpha = (*songsPtr)->head_alpha;
            (*songsPtr)->head_alpha = newSongPtr;
        }
        else {
            previousPtr->next_alpha = newSongPtr;
            newSongPtr->next_alpha = currentPtr;
        } 
        printf("done\n");
        
    }
    else { 
        printf("Memory can not allocated.");
    }
}

glad ploverBOT Jul 19, 2024, 1:00 AM

#

Compiler Output

Program terminated with signal: SIGSEGV

pastel finch Jul 19, 2024, 1:04 AM

#

hazy jackal You don't check if `currentPtr` is NULL. If the list is empty, so `(*songsPtr)->...

oh, right.. thx

#

;compile

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

typedef struct Song {
    char name[25];
    int duration;
    struct Song* next_alpha;
} Song;
typedef Song* SongPtr;

typedef struct SongList {
    int size;
    SongPtr head_alpha;
} SongList;
typedef SongList* SongListPtr;

void insert(SongListPtr*, char[], int);

int main() {
    SongList songs;
    SongListPtr songsPtr = &songs;
    songsPtr->size = 0;
    songsPtr->head_alpha = NULL;
    insert(&songsPtr, "HelloWorld", 150);
    printf("End\n");
    return 0;
}

void insert(SongListPtr* songsPtr, char name[], int duration) {
    SongPtr newSongPtr = (SongPtr)malloc(sizeof(Song));
    if(newSongPtr != NULL) {
        strncpy(newSongPtr->name, name, 24);
        newSongPtr->duration = duration;
        (*songsPtr)->size += 1;

        SongPtr previousPtr = NULL;
        SongPtr currentPtr = (*songsPtr)->head_alpha;
        if(currentPtr == NULL  ||  strcmp(newSongPtr->name, currentPtr->next_alpha->name) < 0) {
            newSongPtr->next_alpha = (*songsPtr)->head_alpha;
            (*songsPtr)->head_alpha = newSongPtr;
        }
        else {
            while(currentPtr->next_alpha != NULL  &&  strcmp(newSongPtr->name, currentPtr->next_alpha->name) > 0) {
                previousPtr = currentPtr;
                currentPtr = currentPtr->next_alpha;
            }

            if(previousPtr == NULL) {
                newSongPtr->next_alpha = (*songsPtr)->head_alpha;
                (*songsPtr)->head_alpha = newSongPtr;
            }
            else {
                previousPtr->next_alpha = newSongPtr;
                newSongPtr->next_alpha = currentPtr;
            } 
        }
        printf("done\n");
        
    }
    else { 
        printf("Memory can not allocated.");
    }
}```

glad ploverBOT Jul 19, 2024, 1:11 AM

#

Program Output

done
End

pastel finch Jul 19, 2024, 1:13 AM

#

uhmm

#

idk why but i dont get any output on my own

#

;compile

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

typedef struct Song {
    char name[25];
    int duration;
    struct Song* next_alpha;
} Song;
typedef Song* SongPtr;

typedef struct SongList {
    int size;
    SongPtr head_alpha;
} SongList;
typedef SongList* SongListPtr;

void insert(SongListPtr*, char[], int);

int main() {
    SongList songs;
    SongListPtr songsPtr = &songs;
    songsPtr->size = 0;
    songsPtr->head_alpha = NULL;
    insert(&songsPtr, "HelloWorld", 150);
    insert(&songsPtr, "Olala", 200);
    printf("End\n");
    return 0;
}

void insert(SongListPtr* songsPtr, char name[], int duration) {
    SongPtr newSongPtr = (SongPtr)malloc(sizeof(Song));
    if(newSongPtr != NULL) {
        strncpy(newSongPtr->name, name, 24);
        newSongPtr->duration = duration;
        (*songsPtr)->size += 1;

        SongPtr previousPtr = NULL;
        SongPtr currentPtr = (*songsPtr)->head_alpha;
        if(currentPtr == NULL  ||  strcmp(newSongPtr->name, currentPtr->next_alpha->name) < 0) {
            newSongPtr->next_alpha = (*songsPtr)->head_alpha;
            (*songsPtr)->head_alpha = newSongPtr;
        }
        else {
            while(currentPtr->next_alpha != NULL  &&  strcmp(newSongPtr->name, currentPtr->next_alpha->name) > 0) {
                previousPtr = currentPtr;
                currentPtr = currentPtr->next_alpha;
            }

            if(previousPtr == NULL) {
                newSongPtr->next_alpha = (*songsPtr)->head_alpha;
                (*songsPtr)->head_alpha = newSongPtr;
            }
            else {
                previousPtr->next_alpha = newSongPtr;
                newSongPtr->next_alpha = currentPtr;
            } 
        }
        printf("done\n");
        
    }
    else { 
        printf("Memory can not allocated.");
    }
}```

glad ploverBOT Jul 19, 2024, 1:16 AM

#

Compiler Output

Program terminated with signal: SIGSEGV

pastel finch Jul 19, 2024, 1:17 AM

#

@hazy jackal it's fine to inserting the first node but i cant insert more

hazy jackal Jul 19, 2024, 1:22 AM

#

You should really use a debugger. It would help instead of guessing where the crash happened.
You check if currentPtr is NULL, but then you use currentPtr->next_alpha without checking.

pastel finch Jul 19, 2024, 1:23 AM

#

oh im done, i corrected my code rn

#

thanks

hazy jackal Jul 19, 2024, 1:25 AM

#

np

#

you're over complicating this though.

oblique anvilBOT Jul 19, 2024, 1:31 AM

#

@pastel finch Has your question been resolved? If so, type !solved :)

pastel finch Jul 19, 2024, 1:37 AM

#

hazy jackal you're over complicating this though.

oh i just used totally different code, i used a different algorithm to implement it

#

i noticed it..

#

!solved

#Whats wrong with following Linked List insertion? (I just put one insertion function call to test)