Printf seems to be overwriting pointer - c

Question

After i call printf for the first time to print out the duplicate it then changes it's mammals pointer to giberish. So when it prints inside the second loop the first mammal comes out fine but then the next in the list is lost. Then every time it exits that loop the next duplicate in the list is lost.
void print_list3() {
Duplicate *next=head3.duppointer;
int i,j;
for(i=0;i<list_length3;i++) {
printf("%c %d %f %f\n",next->species,next->number_of,next->location.lat,next->location.lng);
Mammal mam;
mam=*next->mampointer;
for(j=0;j<next->number_of;j++) {
printf(" %f %f %s\n",mam.location.lat,mam.location.lng,mam.observer.id);
if (mam.pointer!=NULL) {
mam=*mam.pointer;
}
}
if (next!=NULL) {
next=next->duppointer;
}
}
}
Edit: Decided to put all of my code in here, maybe it'll be easier for you guys to find the bug. The problem is with function 2.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "navigation.h"
#include "Mainheader.h"
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <dirent.h>
#include <math.h>
int list_length1=0;
int list_length2=0;
int list_length3=0;
Observer head1;
Mammal head2;
Duplicate head3;
/*
*
*/
int main(int argc, char** argv) {
int choice=0;
run_menu();
scanf("%d",&choice);
while(choice<1 || choice>4) {
printf("Invalid choice\n");
scanf("%d",&choice);
}
if(choice==1) {
function1();
}
else if(choice==2) {
function2();
}
else if(choice==3) {
function3();
}
else if(choice==4) {
printf("Exiting!");
}
return (EXIT_SUCCESS);
}
void run_menu() {
printf("1 - Display cetacean Mammals fn1\n"
"2 - Display without duplicates fn2\n"
"3 - Display Pods without duplicates fn3\n"
"4 - Exit\n");
}
void function1(){
int i=0;
get_directories();
Mammal *next;
next=head2.pointer;
for(i=0;i<list_length2;i++) {
location_calculator(next);
if (next!=NULL) {
next=next->pointer;
}
}
print_reallist();
}
void function2(){
int i=0;
get_directories();
Mammal *next;
next=head2.pointer;
for(i=0;i<list_length2;i++) {
location_calculator(next);
if (next!=NULL) {
next=next->pointer;
}
}
remove_duplicates();
print_list3();
}
void function3(){
}
char get_directories() {
char file1[256];
char file2[256];
char obsid[5];
TD td;
FILE *file_no1;
FILE *file_no2;
Observer* obs=malloc(sizeof(*obs));
Mammal* mam=malloc(sizeof(*mam));
//printf("Please Enter Observer File Path: ");
//scanf("%s",&file1);
strcpy(file1,"/ceri/homes1/j/jsc12/CS237/Assignment/cetaceans/data/observers_2.txt");
file_no1=fopen(file1, "r");
fscanf(file_no1,"%d%d%d%d%d%d",&td.day,&td.month,&td.year,&td.hour,&td.minute,&td.second);
while(fscanf(file_no1,"%s%lf%lf",obs->id,&obs->location.lat,&obs->location.lng)==3) {
obs->timedate=td;
Observer *new;
new=create_observer(obs->id,obs->location,obs->timedate);
add_observer(new);
}
fclose(file_no1);
//printf("Please Enter Sighting File Path: ");
//scanf("%s",&file2);
strcpy(file2,"/ceri/homes1/j/jsc12/CS237/Assignment/cetaceans/data/sightings_2.txt");
file_no2=fopen(file2, "r");
while(fscanf(file_no2,"%4s %c %lf%lf",&obsid,&mam->species,&mam->bearing,&mam->range)==4) {
Observer* obs2=find_observer(obsid);
mam->observer=*obs2;
Mammal *new;
new=create_mammal(mam->observer,mam->species,mam->bearing,mam->range);
add_mammal(new);
}
fclose(file_no2);
}
Mammal* create_mammal (Observer obs,char spec,double bear,double ran){
Mammal* b=malloc(sizeof *b);
b->observer=obs;
b->species=spec;
b->bearing=bear;
b->range=ran;
b->pointer=NULL;
return b;
}
void add_mammal (Mammal *n){
n->pointer=head2.pointer;
head2.pointer=n;
list_length2++;
}
Duplicate* create_duplicate (Duplicate* d){
Mammal mam;
int i;
location average;
average.lat=0;
average.lng=0;
mam=*d->mampointer;
Duplicate* b;
b=malloc(sizeof *b);
b->species=d->mampointer->species;
b->number_of=d->number_of;
for(i=0;i<d->number_of;i++) {
average.lat+=mam.location.lat;
average.lng+=mam.location.lng;
if (mam.pointer!=NULL) {
mam=*mam.pointer;
}
}
average.lat/=d->number_of;
average.lng/=d->number_of;
b->location=average;
b->mampointer=d->mampointer;
b->duppointer=NULL;
return b;
}
void add_duplicate (Duplicate *n){
n->duppointer=head3.duppointer;
head3.duppointer=n;
list_length3++;
}
Observer* create_observer (char id[5],location locat,TD timdat){
Observer* b=malloc(sizeof *b);
strcpy(b->id,id);
b->location=locat;
b->timedate=timdat;
b->pointer=NULL;
return b;
}
void add_observer (Observer *n){
n->pointer=head1.pointer;
head1.pointer=n;
list_length1++;
}
Observer* find_observer(char id[5]) {
Observer *next=head1.pointer;
int i=0;
while(i<list_length1) {
if(strcmp(id,next->id)==0) {
return(next);
}
next=next->pointer;
i++;
}
}
void location_calculator(Mammal* m) {
double obslat=m->observer.location.lat;
double obslng=m->observer.location.lng;
double rbear=(m->bearing*M_PI)/180;
m->location.lat=obslat+(m->range*cos(rbear))/60;
m->location.lng=obslng+(m->range*sin(rbear)/cos((obslat*M_PI)/180))/60;
}
void print_reallist() {
Mammal *next=head2.pointer;
int i;
printf("|==========|==========|==========|==========|\n");
printf("|%-10s|%-10s|%-10s|%-10s|\n","Longitude","Latitude","Species","Observer");
printf("|==========|==========|==========|==========|\n");
for(i=0;i<list_length2;i++) {
if (next->species=='P') {
printf("|%-10lf|%-10lf|%-10s|%-10s|\n",next->location.lat,next->location.lng,"Porpoise",next->observer.id);
if (next!=NULL) {
next=next->pointer;
}
}
else {
printf("|%-10lf|%-10lf|%-10s|%-10s|\n",next->location.lat,next->location.lng,"Dolphin",next->observer.id);
if (next!=NULL) {
next=next->pointer;
}
}
}
printf("|==========|==========|==========|==========|\n");
}
void remove_duplicates() {
int i,j;
double distance;
Mammal *next=head2.pointer;
for(i=0;i<list_length2-1;i++) {
Mammal *check=next->pointer;
Duplicate d;
d.mampointer=NULL;
d.number_of=0;
for(j=0;j<(list_length2-i)-1;j++) {
distance=great_circle(next->location, check->location);
if(distance<=0.02 && next->species==check->species) {
Mammal a=*next;
Mammal b=*check;
a.pointer=d.mampointer;
d.mampointer=&a;
b.pointer=d.mampointer;
d.mampointer=&b;
d.number_of++;
d.number_of++;
}
printf("%f\n",distance);
if (check!=NULL) {
check=check->pointer;
}
}
if(d.mampointer!=NULL) {
add_duplicate(create_duplicate(&d));
}
if (next!=NULL) {
next=next->pointer;
}
}
}
void print_list3() {
Duplicate *next=head3.duppointer;
int i,j;
for(i=0;i<list_length3;i++) {
printf("%c %d %f %f\n",next->species,next->number_of,next->location.lat,next->location.lng);
Mammal mam;
mam=*next->mampointer;
for(j=0;j<next->number_of;j++) {
printf(" %f %f %s\n",mam.location.lat,mam.location.lng,mam.observer.id);
if (mam.pointer!=NULL) {
mam=*mam.pointer;
}
}
if (next!=NULL) {
next=next->duppointer;
}
}
}

Answer 1

There are many problems for the first sight.
It is C, but would be better to avoid name 'new'. Identifier 'location' is a struct name and variable name too. Functions char get_directories() and Observer * find_observer() do not always return.
There are five malloc() but no free() calls.
I am afraid that such function declarations will not guarantee string size, a simple pointer is passed:
Observer * create_observer ( char id[5], ..
Return value of fscanf is not checked. 6 is expected but returns actually 1, because no proper format provided. Perhaps try "%2d%2d%2d%2d%2d%2d"!
fscanf(file_no1,"%d%d%d%d%d%d",&td.day,&td.month,&td.year,&td.hour,&td.minute,&td.second);
Same problem with observer lines. How should fscanf know where the end of string and/or double is? Try for instance "%4s %lf %lf"!
while(fscanf(file_no1,"%s%lf%lf",obs->id,&obs->location.lat,&obs->location.lng)==3) {
String obsid is not scanned properly at this point (remove address operator &):
while(fscanf(file_no2,"%4s %c %lf%lf",&obsid,&mam->species,&mam->bearing,&mam->range)==4) {
Function find_observer() would correctly return NULL if obsid not found. Pointer should not be used in this case, so please check obs2 first:
Observer* obs2=find_observer(obsid);
mam->observer=*obs2;
Could you provide code parts with example input to reproduce problem and resolve issue? I had to reverse engineer even to get following structures to compile at all:
struct Loc { double lat; double lng; };
struct TD { int year; int month; int day; int hour; int minute; int second; };
struct Observer { char id[1024]; Loc location; TD timedate; Observer * pointer; };
struct Mammal { char species; double bearing; double range; Observer observer; Mammal * pointer; Loc location; };
struct Duplicate { Mammal * mampointer; int number_of; char species; Loc location; Duplicate * duppointer; };
And great_circle( Loc, Loc ) function is missing either. Replaced by planar distance calculation instead of supposed spheric:
double great_circle( Loc p0, Loc p1 ) { return pow( ( p0.lat - p1.lat ), 2.0 ) + pow( ( p0.lng - p1.lng ), 2.0 ); }
Without trying duplicates it runs fine for me after fixing errors above.