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Runtime error for using malloc - how to do DMA in C
Posted: Sat Dec 27, 2008 9:13 pm
by Fakhrul Abedin
Hi,
I received Runtime error whenever I use malloc() for Dynamic memory allocation in C. The same code is accepted if I use static array. I don't know if I use malloc in wrong way. How can I do Dynamic memory allocation in C that won't yield RTL?
Here is a sample code of my malloc use
Code: Select all
#include<stdlib.h>
/*Allocating memory for graph*/
G=(int **) malloc((size_t) sizeof(int *)*n);
for(loop=1;loop<=n;loop++){
G[loop]=(int *) malloc((size_t) sizeof(int)*n);
nonaccessible[loop]=1;
}
/*End of allocation*/
Thanks.
Re: Runtime error for using malloc - how to do DMA in C
Posted: Sat Dec 27, 2008 9:19 pm
by mf
You allocate an array of size n (indexed 0 to n-1), but try to write to its elements with indexes 1 to n. The last one doesn't exists, and write to it probably corrupts some of allocator's internal data.
how to do DMA in C
Acronym DMA usually stands for "Direct Memory Access", a thing from OS and hardware worlds.
Re: Runtime error for using malloc - how to do DMA in C
Posted: Sun Dec 28, 2008 10:06 am
by Fakhrul Abedin
Thanks. Yes DMA is an OS staff, I can remember, but here I used it (erroneously) as a shortcut of dynamic memory allocation, not as the acronym of Direct Memory Access.
Your point is right but you will find the RTL even if you use index range between 0 - (n-1) or allocate memory n+1.
My question is if at all malloc funtion can be used in UVA online judege. Or what is the way of dynamic memory allocation in UVA O J.
Regards
Re: Runtime error for using malloc - how to do DMA in C
Posted: Sun Dec 28, 2008 11:19 am
by mf
Yes, malloc() is allowed.
The way you use it is correct, if you either fix your loop to go from 0 to n-1, or allocate n+1 elements.
Re: Runtime error for using malloc - how to do DMA in C
Posted: Mon Dec 29, 2008 6:56 pm
by Fakhrul Abedin
Thank you big brother for your great info.
I am posting here the code for 280 - Vertex where I used malloc, in Linux I don't find any runtime crash but after submission i got RTL. Would you kindly review and help me to find my fault?
Code: Select all
#include<stdio.h>
#include<stdlib.h>
short nonaccessible[101];
int **G,count;
void DFS_VISIT(int n,int i,int adj[]){
int v;
for(v=1;v<=n;v++){
if( !(adj[v]^1) ){
if( !(nonaccessible[v]^1) ){
nonaccessible[v]=0;
count++;
DFS_VISIT(n,v,G[v]);
}
}
}
}
main(){
int n,loop,i,j,visited;
while(scanf("%d",&n) && n){
/*Allocating memory for graph*/
G=(int **) malloc((size_t) sizeof(int *)*(n+1) );
for(loop=1;loop<=n;loop++){
G[loop]=(int *) malloc((size_t) sizeof(int)*(n+1) );
nonaccessible[loop]=1;
}
/*End of allocation*/
/*Generating Graph*/
scanf("%d",&i);
group:
while(scanf("%d",&j) && j){
G[i][j]=1;
}
if(scanf("%d",&i) && i)
goto group;
/*End Generating Graph*/
/*Input of nodes for investigation*/
scanf("%d",&j);
/*Start of investigation*/
while(j--){
scanf("%d",&i);
count=0;
DFS_VISIT(n,i,G[i]);
printf("%d",n-count);
for(loop=1;loop<=n;loop++)
if(nonaccessible[loop])
printf(" %d",loop);
printf("\n");
for(loop=1;loop<=n;loop++)
nonaccessible[loop]=1;
}/*End of Investigation*/
}
}
Re: Runtime error for using malloc - how to do DMA in C
Posted: Mon Dec 29, 2008 10:38 pm
by mf
You don't need malloc there, "int G[101][101];" will do just fine.
If you still want to use malloc, then don't forget that you have to free() every piece of memory that you've malloc()ed.
Re: 280 why TLE?
Posted: Sun Feb 22, 2009 12:57 am
by theharshest
I am getting TLE for following code
Please help
Code: Select all
#include<iostream>
#include<vector>
#include<stack>
using namespace std;
int main()
{
int n,t,k,x,y;
vector< vector<int> > mat; // adjacency matrix
vector<bool> vis; // visited nodes
cin>>n;
while(n!=0)
{
vis.resize(n,0);
scanf("%d",&t);
mat.resize(n);
for(int i=0;i<n;i++)
mat[i].resize(n,-1);
while(t!=0)
{
scanf("%d",&k);
while(k!=0)
{
mat[t-1][k-1]=1;
scanf("%d",&k);
}
scanf("%d",&t);
}
scanf("%d",&x);
while(x--)
{
for(int i=0;i<n;i++)
vis[i]=0;
scanf("%d",&y);
stack<int> s;
for(int i=0;i<n;i++)
if(mat[y-1][i]==1)
{
s.push(i);
break;
}
// applying dfs
while(!s.empty())
{
int tmp=s.top();
vis[tmp]=1;
s.pop();
for(int i=0;i<n;i++)
if(mat[tmp][i]==1 && !vis[i])
s.push(i);
}
vector<int> ans; // stores all unvisited nodes
for(int i=0;i<n;i++)
if(!vis[i])
ans.push_back(i);
printf("%d",(int)ans.size());
sort(ans.begin(),ans.end());
for(int i=0;i<ans.size();i++)
printf(" %d",ans[i]+1);
printf("\n");
}
scanf("%d",&n);
}
}
there is runtime error(SIGSEGV) is coming in my code how can
Posted: Sat Feb 28, 2009 10:43 pm
by shreyarora
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<malloc.h>
int main()
{
int n,i,*c,l,x,k,w=0,j;
long int p,q,args;
char *a,*b,temp;
scanf("%d",&n);
a=(char *)malloc(1000*(sizeof(char)));
b=(char *)malloc(1000*sizeof(char));
c=(int *)malloc(10000*sizeof(int));
for(i=0;i<n;i++)
{
scanf("%s",a);
scanf("%s",b);
l=strlen(a);
q=l/2;
x=strlen(b);
p=x/2;
for(j=0,k=(l-1);j<q;j++,k--)
{
temp=a[j];
a[j]=a[k];
a[k]=temp;
}
for(j=0,k=(x-1);j<p;j++,k--)
{
temp=b[j];
b[j]=b[k];
b[k]=temp;
}
p=atol(a);
q=atol(b);
args=(p+q);
while(args!=0)
{
k=(int)args%10;
c[w]=k;
args=args/10;
w++;
}
c[w]='^';
w++;
}
c[w]='$';
for(i=0;;)
{
if(c
==0)
i++;
else
break;
}
for(i=i;c!='$';i++)
{
if(c=='^')
printf("\n");
else
printf("%d",c);
}
return 0;
}
Re: 280 Vertex TLE Help!!
Posted: Fri Aug 14, 2009 8:05 pm
by calicratis19
AC
Re: 280 Vertex WA Help!!
Posted: Sun Aug 23, 2009 2:23 am
by looserdgr8
Please someone help me. I have run every I/O in this forum. Every thing seems okay. But still i get wrong answer. I use BFS algorithm.
Here is my code:
Code: Select all
Accepted. Array size upgraded to 500
Re: 280 Vertex WA Help!!
Posted: Tue Aug 25, 2009 4:36 pm
by looserdgr8
Please anyone H-E-L-P me. I am now frustrated. Anyone check my code please............>>>
Re: 280 Vertex WA Help!!
Posted: Fri Aug 28, 2009 11:38 pm
by looserdgr8
Anyone please help me.
Re: 280 Vertex WA Help!!
Posted: Wed Sep 02, 2009 3:38 pm
by calicratis19
@looserdgr8 increase the size of the defined constant 'size'. u will get ac.
Re: 280 Vertex WA Help!!
Posted: Fri Sep 04, 2009 12:38 am
by looserdgr8
Thanx calicratis19. Its AC
Re: 280 Vertex WA Help!!
Posted: Fri Sep 04, 2009 7:59 pm
by calicratis19
@looserdgr8, u should remove your code.thanks.