Undefined reference error

**pshirishreddy** · 08-02-2009

hello,

I get the follow error when i compile the code

Code:

fctr.c: In function ‘main’:
fctr.c:17: warning: format ‘%ld’ expects type ‘long int’, but argument 2 has type ‘int’
/tmp/ccfw9Xlk.o: In function `num_zeroes':
fctr.c:(.text+0x33): undefined reference to `pow'
fctr.c:(.text+0x3e): undefined reference to `floor'
fctr.c:(.text+0x76): undefined reference to `pow'
/tmp/ccfw9Xlk.o: In function `main':
fctr.c:(.text+0x100): undefined reference to `numzeroes'
collect2: ld returned 1 exit status

My code is

Code:

#include <stdio.h>
#include <math.h>
long int num_zeroes(int num){
	long int sum = 0;
	int n;
	for(n=0;num<pow(5,n);n++)
		sum = sum + floor(num/pow(5,n));
	return sum;
}
main(){
	int cases,i;
	long int num[100000];
	scanf("%d",&cases);
	for(i=0; i<cases; i++)
		scanf("%ld",&num[i]);
	for(i=0;i<cases;i++)
		printf("%ld",num_zeroes(num[i]));
}

can any one guide me where i am going wrng

**GL.Sam** · 08-02-2009

printf("%ld",numzeroes(num[i]));

Your actual function name contains underscore.

**MK27** · 08-02-2009

One of these is due to a spelling mistake, I'll let you guess which one.

Most of the others may be due to not linking to the math library. With gcc, if you #include <math.h>, you must also compile with the -lm switch. I don't know how you do that with other compilers.

The %ld thing may be just because that is more of an output (ie, printf, not scanf) parameter. Try %d.

**pshirishreddy** · 08-02-2009

Even after i correct the function name i end up with errors like undefined reference to
/tmp/ccfw9Xlk.o: In function `num_zeroes':
fctr.c

.text+0x33): undefined reference to `pow'
fctr.c

.text+0x3e): undefined reference to `floor'
fctr.c

.text+0x76): undefined reference to `pow'

**pshirishreddy** · 08-02-2009

Any idea on why the linking doesn't happen, though it solves the problem i am a little confused on why it doesnt compile the normal way. I never used the -lm switch before what does the switch do, i am unable to locate the switch functions even in the man pages ...

**rags_to_riches** · 08-02-2009

-lm tells the linker to include the math library when linking, so that it can find the definitions of those functions it's not finding.

**pshirishreddy** · 08-02-2009

So, are there switches for every library like the math library ?

**tabstop** · 08-02-2009

Originally Posted by pshirishreddy

So, are there switches for every library like the math library ?

-l just means "use the library that follows now". The math library is, for whatever reason, called "m". Hence -lm. The C runtime library (which is called "c") is linked in by default, but any other library you intend to use should be linked in. (For instance, if you were using OpenGL, you'd probably have -lopengl in your command line.)

**pshirishreddy** · 08-02-2009

thanks tabstop, where can i get the list of switches for the corresponding libraries ?

**tabstop** · 08-02-2009

Originally Posted by pshirishreddy

thanks tabstop, where can i get the list of switches for the corresponding libraries ?

There aren't any. -l is the only switch there is, and you put the name of the library after the l. Presumably you know which libraries your program is intending to use, so you put those there.

**MK27** · 08-02-2009

Originally Posted by pshirishreddy

thanks tabstop, where can i get the list of switches for the corresponding libraries ?

There isn't one. Generally, if you are using a non-standard library, you have to look at some documentation first and hopefully it will say. For example:

Mathematics: <math.h>

but math.h is kind of an exception, since most people don't need instructions for pow().

**pshirishreddy** · 08-02-2009

thank you..

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