Thread: Simple parameter mismatch error

I have a class called File with the following method:

Code:

template <class T>
bool File::writeBytes(T *obj)
{
 if(fwrite(obj, sizeof(T), 1, file) < 1)
  return false;
  
 return true;
}

I call the method as follows:

Code:

class foo
{
 public:
  int a;
  string b;
};

...

 File file("test");
 foo f;
 f.a = 4545;
 f.b = "32453452354";
 file3.writeBytes(&f);

But I get the following error when compiling:
/usr/people/cs/student/ymalik/axesone/main.cc:30: undefined reference to `bool File::writeBytes<foo>(foo*)'

But I do have it since the method is templated. Can someone please tell me what is wrong?

Thanks.

Is the function defination in the header file or in another source file that you are linking in?

Well, here's my class definition:

Code:

#ifndef _FILE_H_
#define _FILE_H_

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

using namespace std;

class File
{
 private:
  FILE *file;
  string fileName;

 public:
  File(string);
  File(string, string);
  ~File();
  bool readLine(string &);
  
  template <class T>
  void readBytes(T *);
  
  bool writeLine(string);
  
  template <class T>
  bool writeBytes(T *);

  bool reName(string);
  bool isThere();
};

#endif

I have .h file with the definition, a .cc file with the implementation, and a tester program.

Try putting all the template function definations in the header. Most compilers require this.

Ok, thanks, that worked, but why did the compiler complain in the tester program and not the class file?

Because it didn't run into a problem until it tried to write the function and link it.