I have second level include that is giving me grief:
Undefined first referenced
symbol in file
function2 /var/tmp//ccAPaWbT.o
ld: fatal: symbol referencing errors. No output written to run
collect2: ld returned 1 exit status
Main file:
#include "functions02.c"
int main(){
int x = funcion2();
}
functions02.c file:
#ifndef FUNCTIONS02_C
#define FUNCTIONS02_C
int funcion2();
#if __INCLUDE_LEVEL__ == 0
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include "functions01.c"
int main() {
return function2();
}
#endif
int function2()
return function1();
}
#endif
functions01.c file:
#ifndef FUNCTIONS01_C
#define FUNCTIONS01_C
int funcion1();
#if __INCLUDE_LEVEL__ == 0
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
int main() {
return function1();
}
#endif
int function1()
return 10;
}
#endif
I am assuming that this can be fixed manipulated using __INCLUDE_LEVEL__ or manipulating linking on gcc compiling but I can't find forking variant.
First of all is it possible to achieve what I am looking for without putting functions in external header files?
Second what would be the correct way of doing it?
EDIT:
I realized that I had forgotten to add function dependencies to them. That is the includes which are used by functions can not be excluded by adding them just next to main function warped in exclusion if close.
Yes, it is possible to include / exclude any part of the code using compile time flags (and in the code using #if's) as you are trying to do.
In your case, I assume you have not defined __INCLUDE_LEVEL__ flag, hence the linker is not able to find funciton2, so the error.
If you define it, you will have three "main()" :-), it will fail again. So, you need to rework your code a bit.
Also, #include'ing a "C" file is not advisable and not used in practice. I assume you are just trying to experiment & learn, which is fine.
Related
My compiler (GCC) is giving me the warning:
warning: implicit declaration of function
Why is it coming?
You are using a function for which the compiler has not seen a declaration ("prototype") yet.
For example:
int main()
{
fun(2, "21"); /* The compiler has not seen the declaration. */
return 0;
}
int fun(int x, char *p)
{
/* ... */
}
You need to declare your function before main, like this, either directly or in a header:
int fun(int x, char *p);
The right way is to declare function prototype in header.
Example
main.h
#ifndef MAIN_H
#define MAIN_H
int some_main(const char *name);
#endif
main.c
#include "main.h"
int main()
{
some_main("Hello, World\n");
}
int some_main(const char *name)
{
printf("%s", name);
}
Alternative with one file (main.c)
static int some_main(const char *name);
int some_main(const char *name)
{
// do something
}
When you do your #includes in main.c, put the #include reference to the file that contains the referenced function at the top of the include list.
e.g. Say this is main.c and your referenced function is in "SSD1306_LCD.h"
#include "SSD1306_LCD.h"
#include "system.h" #include <stdio.h>
#include <stdlib.h>
#include <xc.h>
#include <string.h>
#include <math.h>
#include <libpic30.h> // http://microchip.wikidot.com/faq:74
#include <stdint.h>
#include <stdbool.h>
#include "GenericTypeDefs.h" // This has the 'BYTE' type definition
The above will not generate the "implicit declaration of function" error, but below will-
#include "system.h"
#include <stdio.h>
#include <stdlib.h>
#include <xc.h>
#include <string.h>
#include <math.h>
#include <libpic30.h> // http://microchip.wikidot.com/faq:74
#include <stdint.h>
#include <stdbool.h>
#include "GenericTypeDefs.h" // This has the 'BYTE' type definition
#include "SSD1306_LCD.h"
Exactly the same #include list, just different order.
Well, it did for me.
You need to declare the desired function before your main function:
#include <stdio.h>
int yourfunc(void);
int main(void) {
yourfunc();
}
When you get the error: implicit declaration of function it should also list the offending function. Often this error happens because of a forgotten or missing header file, so at the shell prompt you can type man 2 functionname and look at the SYNOPSIS section at the top, as this section will list any header files that need to be included. Or try http://linux.die.net/man/ This is the online man pages they are hyperlinked and easy to search.
Functions are often defined in the header files, including any required header files is often the answer. Like cnicutar said,
You are using a function for which the compiler has not seen a
declaration ("prototype") yet.
If you have the correct headers defined & are using a non GlibC library (such as Musl C) gcc will also throw error: implicit declaration of function when GNU extensions such as malloc_trim are encountered.
The solution is to wrap the extension & the header:
#if defined (__GLIBC__)
malloc_trim(0);
#endif
This error occurs because you are trying to use a function that the compiler does not understand. If the function you are trying to use is predefined in C language, just include a header file associated with the implicit function.
If it's not a predefined function then it's always a good practice to declare the function before the main function.
Don't forget, if any functions are called in your function, their prototypes must be situated above your function in the code. Otherwise, the compiler might not find them before it attempts to compile your function. This will generate the error in question.
The GNU C compiler is telling you that it can find that particular function name in the program scope. Try defining it as a private prototype function in your header file, and then import it into your main file.
I think the question is not 100% answered. I was searching for issue with missing typeof(), which is compile time directive.
Following links will shine light on the situation:
https://gcc.gnu.org/onlinedocs/gcc-5.3.0/gcc/Typeof.html
https://gcc.gnu.org/onlinedocs/gcc-5.3.0/gcc/Alternate-Keywords.html#Alternate-Keywords
as of conculsion try to use __typeof__() instead. Also gcc ... -Dtypeof=__typeof__ ... can help.
I have two source files: one I want to test via asserts, the second containing the asserts.
My problem is that I do not want the testing to be run each time the program itself is run, so is there a way to toggle assert testing on or off depending on a makefile argument?
Or will I have to create another source file, containing both the code I want to test and the assert testing itself?
man 3 assert says
If the macro NDEBUG is defined at the moment <assert.h> was last
included, the macro assert() generates no code, and hence does
nothing at all.
gcc ... -DNDEBUG is intended for a release build, and will not do anything in assert().
My problem is that I do not want the testing to be run each time the
program itself is run
If only the second file you mention contains the assert statements, why would the test code be run when you run the program?
Here is a typical way to divide the code for a module Foo containing a function Bar and its unit test:
Foo.h
#ifndef FOO_H
#define FOO_H
int Foo_Bar(int i);
#endif
Foo.c
#include "Foo.h"
int Foo_Bar(int i)
{
/*to be implemented*/
return -1;
}
FooTest.c
#include "Foo.h"
#include <assert.h>
int main(void)
{
assert(Foo_Bar(0) == 0);
return 0;
}
myprog.c
#include "Foo.h"
int main(void)
{
int bar = Foo_Bar(0);
/*...*/
return 0;
}
My compiler (GCC) is giving me the warning:
warning: implicit declaration of function
Why is it coming?
You are using a function for which the compiler has not seen a declaration ("prototype") yet.
For example:
int main()
{
fun(2, "21"); /* The compiler has not seen the declaration. */
return 0;
}
int fun(int x, char *p)
{
/* ... */
}
You need to declare your function before main, like this, either directly or in a header:
int fun(int x, char *p);
The right way is to declare function prototype in header.
Example
main.h
#ifndef MAIN_H
#define MAIN_H
int some_main(const char *name);
#endif
main.c
#include "main.h"
int main()
{
some_main("Hello, World\n");
}
int some_main(const char *name)
{
printf("%s", name);
}
Alternative with one file (main.c)
static int some_main(const char *name);
int some_main(const char *name)
{
// do something
}
When you do your #includes in main.c, put the #include reference to the file that contains the referenced function at the top of the include list.
e.g. Say this is main.c and your referenced function is in "SSD1306_LCD.h"
#include "SSD1306_LCD.h"
#include "system.h" #include <stdio.h>
#include <stdlib.h>
#include <xc.h>
#include <string.h>
#include <math.h>
#include <libpic30.h> // http://microchip.wikidot.com/faq:74
#include <stdint.h>
#include <stdbool.h>
#include "GenericTypeDefs.h" // This has the 'BYTE' type definition
The above will not generate the "implicit declaration of function" error, but below will-
#include "system.h"
#include <stdio.h>
#include <stdlib.h>
#include <xc.h>
#include <string.h>
#include <math.h>
#include <libpic30.h> // http://microchip.wikidot.com/faq:74
#include <stdint.h>
#include <stdbool.h>
#include "GenericTypeDefs.h" // This has the 'BYTE' type definition
#include "SSD1306_LCD.h"
Exactly the same #include list, just different order.
Well, it did for me.
You need to declare the desired function before your main function:
#include <stdio.h>
int yourfunc(void);
int main(void) {
yourfunc();
}
When you get the error: implicit declaration of function it should also list the offending function. Often this error happens because of a forgotten or missing header file, so at the shell prompt you can type man 2 functionname and look at the SYNOPSIS section at the top, as this section will list any header files that need to be included. Or try http://linux.die.net/man/ This is the online man pages they are hyperlinked and easy to search.
Functions are often defined in the header files, including any required header files is often the answer. Like cnicutar said,
You are using a function for which the compiler has not seen a
declaration ("prototype") yet.
If you have the correct headers defined & are using a non GlibC library (such as Musl C) gcc will also throw error: implicit declaration of function when GNU extensions such as malloc_trim are encountered.
The solution is to wrap the extension & the header:
#if defined (__GLIBC__)
malloc_trim(0);
#endif
This error occurs because you are trying to use a function that the compiler does not understand. If the function you are trying to use is predefined in C language, just include a header file associated with the implicit function.
If it's not a predefined function then it's always a good practice to declare the function before the main function.
Don't forget, if any functions are called in your function, their prototypes must be situated above your function in the code. Otherwise, the compiler might not find them before it attempts to compile your function. This will generate the error in question.
The GNU C compiler is telling you that it can find that particular function name in the program scope. Try defining it as a private prototype function in your header file, and then import it into your main file.
I think the question is not 100% answered. I was searching for issue with missing typeof(), which is compile time directive.
Following links will shine light on the situation:
https://gcc.gnu.org/onlinedocs/gcc-5.3.0/gcc/Typeof.html
https://gcc.gnu.org/onlinedocs/gcc-5.3.0/gcc/Alternate-Keywords.html#Alternate-Keywords
as of conculsion try to use __typeof__() instead. Also gcc ... -Dtypeof=__typeof__ ... can help.
In the K&R book (p59) (edit: second edition, covering ANSI C), it is suggested that it is easier to split larger projects into multiple files. In each file, several libraries are included at the top as usual: e.g. getop.c needs stdio.h, and so does stack.c and so does main.c.
The snippets are something like this:
//main.c
#include <stdio.h>
#include <stdlib.h>
#include "calc.h"
int main(void)
{
//etc
}
//getop.c
#include <stdio.h>
#include <ctype.h>
#include "calc.h"
getop()
{
/*code*/
}
//stack.c
#include <stdio.h>
#include "calc.h"
void push(double val)
{
//code
}
I am having trouble figuring out how including the standard libraries several times in a project works. Of course, for the custom .c files to be able to access built in functions, we need to include #include <header.h> so that they are aware of the existence of printf() and getchar() and so on, but wouldn't this approach increase the size of the final program if stdio.h is included four times instead of once ( if everything was placed in one file)?
K&R does point out that splitting a program over several files eventually makes it more difficult to maintain all the .h files.
I suppose what I am really asking is how does the compiler figure out the problem of one library being #included several times in a project.
I have read up on using include guards, but it seems that is not needed for this implementation, as they deal with ensuring that identical bits of code aren't included twice, as in:
File "module.h"
#ifndef MODULE_H
#define MODULE_H
struct foo {
int member;
};
#endif /* MODULE_H */
File "mod2.h"
#include "module.h"
File "prog.c"
#include "module.h"
#include "mod2.h"
refs
I suppose what I am really asking is how does the compiler figure out the problem of one library being #included several times in a project.
you don't include a library by #include <stdio.h>, you just include it's declarations, so the compiler knows what functions exists. The linker takes care of including a library and putting everything together.
Because they use something called include guards, suppose your own include files where to be included more than once, then you can do this
MyHeader.h
#ifndef MY_HEADER_H
#define MY_HEADER_H
/* file content goes here */
#endif /* MY_HEADER_H */
Then you have another header
**AnotherHeader.h**
#ifndef MY_ANOTHER_HEADER_H
#define MY_ANOTHER_HEADER_H
#include "MyHeader.h"
/* file content goes here */
#endif /* MY_ANOTHER_HEADER_H */
and in your program
main.c
/*
* MY_HEADER_H is undefined so it will be defined and MyHeader.h contents
* will be included.
*/
#include "MyHeader.h"
/*
* MY_HEADER_H is defined now, so MyHeader.h contents will not be included
*/
#include "AnotherHeader.h"
int main()
{
return 0;
}
Since the included files are only included once per compilation unit the resulting binary size will not increase, besides the inclusion of header files only increases the compiled file size when for example there are string literals declared in those headers, otherwise they only provide information to the compiler about how to call a given function, i.e. how to pass parameters to it and how to store it's returned value.
I'm trying to understand how global variables and functions work in C. My program compiles and works fine with gcc, but does not compile with g++. I have the following files:
globals.h:
int i;
void fun();
globals.c:
#include "stdlib.h"
#include "stdio.h"
void fun()
{
printf("global function\n");
}
main.c:
#include "stdlib.h"
#include "stdio.h"
#include "globals.h"
void myfun();
int main()
{
i=1;
myfun();
return 0;
}
And finally, myfun.c:
#include "stdlib.h"
#include "stdio.h"
#include "globals.h"
void myfun()
{
fun();
}
I get the following error when compiling with g++:
/tmp/ccoZxBg9.o:(.bss+0x0): multiple definition of `i'
/tmp/ccz8cPTA.o:(.bss+0x0): first defined here
collect2: ld returned 1 exit status
Any ideas why? I would prefer to compile with g++.
Every file you include globals.h from will define "int i".
Instead, put "extern int i;" into the header file and then put the actual definition of "int i = 1;" in globals.c.
Putting header guards around globals.h would be sensible too.
Edit: In answer to your question its because a #include works kind of like a cut and paste. It pastes the contents of the included file into the c file that you are calling include from. As you include "globals.h" from main.c and myfun.c you define int i = 1 in both files. This value, being global, gets put into the table of linkable values. If you have the same variable name twice then the linker won't be able to tell which one it needs and you get the error you are seeing. Instead by adding extern on the front in the header file you are telling each file that "int i" is defined somewhere else. Obviously, you need to define it somewhere else (and ONLY in one place) so defining it in globals.c makes perfect sense.
Hope that helps :)
I would add an include guard in your globals file
#ifndef GLOBALS_H
#define GLOBALS_H
int i;
void fun();
#endif
Edit: Change your globals to be like this (using extern as the other answer describes)
globals.h
extern int i;
extern void fun();
globals.c
#include "stdlib.h"
#include "stdio.h"
int i;
void fun()
{
printf("global function\n");
}
I compiled it with
g++ globals.c main.c myfun.c
and it ran ok
Several things wrong here; several other things highly recommended:
globals.h:
#ifndef GLOBALS_H
#define GLOBALS_H
extern int my_global;
#ifdef __cplusplus
extern "C" {
#endif
void fun();
#ifdef __cplusplus
}
#endif
#endif
/* GLOBALS_H */
globals.c:
#include <stdlib.h>
#include <stdio.h>
#include "globals.h"
int my_global;
void fun()
{
printf("global function: %d\n", my_global);
}
main.c:
#include <stdlib.h>
#include <stdio.h>
#include "globals.h"
void myfun();
int main()
{
my_global=1;
myfun();
return 0;
}
void myfun()
{
fun();
}
You should declare "extern int myvar" in your header, and actually allocate "int myvar" in one and only one .c file.
You should include "globals.h" in every file that uses "myvar" - including the file where it's allocated.
Especially if you're planning on mixing C and C++ modules, you should use 'extern "C"' to distinguish non-C++ functions.
System headers should be "#include <some_header.h>"; your own headers should use quotes (#include "myheader.h") instead.
Short variable names like "i" might be OK for a strictly local variable (like a loop index), but you should always use longer, descriptive names whenever you can't avoid using a global variable.
I added a "printf" for my_global.
'Hope that helps!
I had this problem when porting some old C code to C++. The problem was it was a project that was connected to a database, and i wanted to port the database to c++ but not the rest. The database pulled in some C dependencies that couldn't be ported, so i needed the C code that overlapped both the database and the other project to compile in g++ as well as gcc...
The solution to this problem is to define all variables as extern in the .h file. then when you compile in either gcc or g++ it will report symbols missing in the .c files. So edit the .c files in the error messages and insert the declaration into all the .c files that need the variables. Note: you may have to declare it in multiple .c files, which is what threw me and why I was stuck on this problem for ages.
Anyway this solved my problem and the code compiles cleanly under both gcc and g++ now.