c programming on linux platform

ibabhelix · 09-30-2009, 04:37 AM

@lemon09
thank you so much its working now.
thanks [

]

lemon09 · 09-30-2009, 04:43 AM

all the best............

have a happy journey...

ibabhelix · 10-08-2009, 03:05 AM

hi guys.
in my program when i compiled i got this warning:

warning: function returns address of local variable

the program is running succesfully but i want to know how to correct this warning.

please help me

Nylex · 10-08-2009, 03:25 AM

Quote:

Originally Posted by ibabhelix

warning: function returns address of local variable

Which function? Can you post the problem code? Does the function in question return a pointer? If so, you shouldn't return a pointer to a variable that's declared on the stack in that function. The reason is that when the function returns, these variables are removed from the stack and so that memory should no longer be used by your program.

lutusp · 10-08-2009, 03:37 AM

Quote:

Originally Posted by ibabhelix

hi guys.
in my program when i compiled i got this warning:

warning: function returns address of local variable

the program is running succesfully but i want to know how to correct this warning.

please help me

You don't want to return the address of a local variable, because that variable only exists within the function. This is a recipe for trouble.

Code:

please help me

Sorry, my crystal ball is cloudy right now ... try again later ... when you post your code.

smeezekitty · 10-08-2009, 12:50 PM

Quote:

Originally Posted by ibabhelix

hi guys.
in my program when i compiled i got this warning:

warning: function returns address of local variable

the program is running succesfully but i want to know how to correct this warning.

please help me

its probably not good
thats one of those warnings you actually have to worry about
try decalring the variables that its returning as static

i92guboj · 10-08-2009, 01:15 PM

Or better yet, pass a pointer to the variable to the function and declare it out of the function. Or, if it's a simple enough type, just make the function return that data type, and call it as value=func(...);

But, as said, no code = no concrete answer.

ibabhelix · 10-09-2009, 12:41 AM

here is the code

Quote:

char* TorsionCheck()
{
int i,j;
float r1[3][1],r2[3][1],r3[3][1],n1[3][1],n2[3][1];
float mn1,mn2;
float a1,a2,a3;
float b1,b2,b3;
float k,l;
float n1n2,teta;
float n1t[1][3];
float s[3][1],sign;
char returnValue[80];

//gettin the vectors

for(i=0;i<3;i++)
{
for(j=0;j<1;j++)
{
r1[i][j]=a[i][j]-b[i][j];
}
}
for(i=0;i<3;i++)
{
for(j=0;j<1;j++)
{
r2[i][j]=c[i][j]-b[i][j];
}
}

//gettin the normal
//printf("the normal n1=");

n1[0][0]=r1[1][0]*r2[2][0]-r1[2][0]*r2[1][0];
n1[0][1]=r1[2][0]*r2[0][0]-r1[0][0]*r2[2][0];
n1[0][2]=r1[0][0]*r2[1][0]-r1[1][0]*r2[0][0];

a1=n1[0][0]*n1[0][0];
a2=n1[0][1]*n1[0][1];
a3=n1[0][2]*n1[0][2];
mn1=sqrt(a1+a2+a3);

//printf("magnitude of n1=%f",mn1);
//printf("the vector r3=\n");
for(i=0;i<3;i++)
{
for(j=0;j<1;j++)
{
r3[i][j]=b[i][j]-d[i][j];
}
}

//gettin the normal
//printf("the normal n2=");

n2[0][0]=r2[1][0]*r3[2][0]-r2[2][0]*r3[1][0];
n2[0][1]=r2[2][0]*r3[0][0]-r2[0][0]*r3[2][0];
n2[0][2]=r2[0][0]*r3[1][0]-r2[1][0]*r3[0][0];

b1=(n2[0][0])*(n2[0][0]);
b2=(n2[0][1])*(n2[0][1]);
b3=(n2[0][2])*(n2[0][2]);
mn2=sqrt(b1+b2+b3);
//printf("magnitude of n2=%f",mn2);

//dot product for obtaining the angle //

n1n2=n1[0][0]*n2[0][0]+n1[1][0]*n2[1][0]+n1[2][0]*n2[2][0];
//printf("\n%f",n1n2);
teta=acos(n1n2/(mn1*mn2))*57.29578;
// printf("\nteta=%f",teta);

//scalar triplet product

s[0][0]=n1[1][0]*n2[2][0]-n1[2][0]*n2[1][0];
s[0][1]=n1[2][0]*n2[0][0]-n1[0][0]*n2[2][0];
s[0][2]=n1[0][0]*n2[1][0]-n1[1][0]*n2[0][0];

sign=s[0][0]*r2[0][0]+s[1][0]*r2[1][0]+s[2][0]*r2[2][0];

//printf("\n%f",sign);
sprintf(returnValue, "Theta Value = %s %f. \n", ((sign>0) ? " " : "-"), teta);
// sprintf(returnValue, "Theta Value = %f", teta);

/* if(sign>0)
printf("\nThe torsional angle is positive");
else
printf("\nThe torsional angle is positive");*/
return returnValue;
}

ibabhelix · 10-09-2009, 12:42 AM

here is the code

Quote:

char* TorsionCheck()
{
int i,j;
float r1[3][1],r2[3][1],r3[3][1],n1[3][1],n2[3][1];
float mn1,mn2;
float a1,a2,a3;
float b1,b2,b3;
float k,l;
float n1n2,teta;
float n1t[1][3];
float s[3][1],sign;
char returnValue[80];

//gettin the vectors

for(i=0;i<3;i++)
{
for(j=0;j<1;j++)
{
r1[i][j]=a[i][j]-b[i][j];
}
}
for(i=0;i<3;i++)
{
for(j=0;j<1;j++)
{
r2[i][j]=c[i][j]-b[i][j];
}
}

//gettin the normal
//printf("the normal n1=");

n1[0][0]=r1[1][0]*r2[2][0]-r1[2][0]*r2[1][0];
n1[0][1]=r1[2][0]*r2[0][0]-r1[0][0]*r2[2][0];
n1[0][2]=r1[0][0]*r2[1][0]-r1[1][0]*r2[0][0];

a1=n1[0][0]*n1[0][0];
a2=n1[0][1]*n1[0][1];
a3=n1[0][2]*n1[0][2];
mn1=sqrt(a1+a2+a3);

//printf("magnitude of n1=%f",mn1);
//printf("the vector r3=\n");
for(i=0;i<3;i++)
{
for(j=0;j<1;j++)
{
r3[i][j]=b[i][j]-d[i][j];
}
}

//gettin the normal
//printf("the normal n2=");

n2[0][0]=r2[1][0]*r3[2][0]-r2[2][0]*r3[1][0];
n2[0][1]=r2[2][0]*r3[0][0]-r2[0][0]*r3[2][0];
n2[0][2]=r2[0][0]*r3[1][0]-r2[1][0]*r3[0][0];

b1=(n2[0][0])*(n2[0][0]);
b2=(n2[0][1])*(n2[0][1]);
b3=(n2[0][2])*(n2[0][2]);
mn2=sqrt(b1+b2+b3);
//printf("magnitude of n2=%f",mn2);

//dot product for obtaining the angle //

n1n2=n1[0][0]*n2[0][0]+n1[1][0]*n2[1][0]+n1[2][0]*n2[2][0];
//printf("\n%f",n1n2);
teta=acos(n1n2/(mn1*mn2))*57.29578;
// printf("\nteta=%f",teta);

//scalar triplet product

s[0][0]=n1[1][0]*n2[2][0]-n1[2][0]*n2[1][0];
s[0][1]=n1[2][0]*n2[0][0]-n1[0][0]*n2[2][0];
s[0][2]=n1[0][0]*n2[1][0]-n1[1][0]*n2[0][0];

sign=s[0][0]*r2[0][0]+s[1][0]*r2[1][0]+s[2][0]*r2[2][0];

//printf("\n%f",sign);
sprintf(returnValue, "Theta Value = %s %f. \n", ((sign>0) ? " " : "-"), teta);
// sprintf(returnValue, "Theta Value = %f", teta);

/* if(sign>0)
printf("\nThe torsional angle is positive");
else
printf("\nThe torsional angle is positive");*/
return returnValue;
}

Nylex · 10-09-2009, 12:54 AM

Please use [code] tags in future, rather than [quote] tags. This will allow you to preserve indentation when posting code.

Your problem seems to be as I described earlier. i92guboj posted a solution, so please try it.

Edit:

float r1[3][1]

If you're declaring arrays of length 3, why do you have another "dimension" of length 1? Surely that second index is superfluous?

pixellany · 10-09-2009, 07:51 AM

Moved: This thread is more suitable in <Programming> and has been moved accordingly to help your thread/question get the exposure it deserves.

johnsfine · 10-09-2009, 08:15 AM

Quote:

Originally Posted by ibabhelix

here is the code

char* TorsionCheck()
{
. . .
char returnValue[80];
. . .
return returnValue;
}

First, do you understand why the above is wrong?

Arrays in C are passed and returned by address, not by value. So when you return returnValue, you are returning just a pointer to the 80 char array, not a copy of it.

That 80 char array goes out of scope when the function exits, so its memory may be reused by any later function that is called.

Because TorsionCheck has so much local storage, your program apparently works despite this serious bug. The compiler happened to allocate returnValue far enough down the stack and you then called only functions that use less stack, so the value did not get clobbered before you used it. Any of that could be affected by minor changes almost anywhere in your program. So this bug could suddenly make your program fail after some change that may not appear to relate in any way to the actual bug.

Once you understand why the code is wrong, then you should fix it. Depending on the rest of your program, there are several different approaches to fixing this bug. Some of them are:

1) Use malloc: Instead of
char returnValue[80];
use
char* returnValue = (char*)malloc(80);

If you do that, then freeing the allocated memory becomes the responsibility of the calling code.

If TorsionCheck is called only once per run of your program and/or the resulting char array is needed until nearly the end of the program, it is common and OK to just forget about freeing the memory, because when the program exits it makes no difference whether such allocations were internally freed.

But in other situations, it is important for the calling code to know that it "owns" the returned memory and must use the free() function to release it when it is no longer needed.

2) Declare the char[80] in the calling code and pass the address into TorsionCheck, rather than out of it.

3) Make the return value static: If TorsionCheck is called only once, or if the caller of TorsionCheck is always done using the result before it calls TorsionCheck again, you can change
char returnValue[80];
to
static char returnValue[80];

Sergei Steshenko · 10-09-2009, 10:08 AM

Quote:

Originally Posted by ibabhelix

is there a solution for the above problem ?
please help me.

Yes, there is - learn "C" - your problem has nothing to do with Linux or any other OS in particular.

...

Regarding your code

Code:

float r1[3][1],r2[3][1],r3[3][1],n1[3][1],n2[3][1];

- what is the exact reason for the second index to be 1 ?

ibabhelix · 10-12-2009, 01:15 AM

thank u so much
m still a learner i'm learning slowly.
thank u johnsfine and Sergei Steshenko for helping me.

smeezekitty · 10-12-2009, 01:32 AM

Quote:

Originally Posted by johnsfine

First, do you understand why the above is
If TorsionCheck is called only once per run of your program and/or the resulting char array is needed until nearly the end of the program, it is common and OK to just forget about freeing the memory, because when the program exits it makes no difference whether such allocations were internally freed.

WTF? that is called a MEMORY LEAK and is very bad programming practice and telling a newbie that its is ok is just an outright stupid thing to do.