I have two C files namely 'Main.c' and 'algo.c'. The main.c file contains an array called the index_array and looks as follows:
#include <stdlib.h>
#include <stddef.h>
#include <stdio.h>
#include "Main.c"
int algo();
int main(){
int index_array []= {1,2,3,4,5,6};
algo(index_array); //to call the function from the other file
return 0;
}
The other file looks like this:
#include <stdlib.h>
#include <stddef.h>
#include <stdio.h>
int algo(int index_array){
///contains an algorithm to perform an operation using the array index from the Main.c file
}
Now what I have a doubt is on how do I get access to the array index_array[ ] from the algo.c file? The way I have tried it in the alog.c file does not give me access to it. It instead gives an error saying multiple declarations of 'algo'.
Could somebody give me an idea on this please?
The easiest approach will be to change the algo() function signature to accept two parameters, the array itself and the size. Something like
int algo(int *index_array, int size) { ....
That said, you should change your forward declaration to match the signature of the function definition.
Now, you can call algo from the main.c file like
algo(index_array, sizeof(index_array)/sizeof(index_array[0]));
Note: Please remove #include "Main.c" from your code. Source files are meant to be compiled and linked together to generate the binary.
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.
In the same line I get two errors:
/path/idt.c:15: multiple definition of 'initialize_idt'
and
/path/idt.c:15: first defined here
and I'm baffled as to why this might be. I'm declaring in the .h, defining in the .c, and calling in another .c. Every example I've seen doesn't properly #include, but I don't see a problem in my implementation.
/***idt.c***/
#include "idt.h"
#include "x86_desc.h"
void initialize_idt(){
//code
}
/*********/
/***idt.h***/
#ifndef _IDT_H
#define _IDT_H
#include "types.h"
void initialize_idt(void);
#endif
/*********/
/***kernel.c***/
#include "idt.h"
#include "x86_desc.h
void entry(){
initialize_idt();
}
/*********/
EDIT:
The code is very long, it would be a lot to post all at once. I tried changing _IDT_H to a long random sequence and that doesn't seem to fix the problem. grep -rnwe 'initialize_idt' returns:
idt.c:7:/* initialize_idt adding this to fix highlighting->*/
idt.c:15:void initialize_idt(){
idt.h:14:void initialize_idt(void);
Binary file idt.o matches
kernel.c:141: initialize_idt();
Binary file kernel.o matches
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'm writing a program for vocabulary training, for myself. And the program itself should be available in different languages, atm in German and English.
What I want is to have a main file which manage all and two separate files for the functions in the right language.
I compile all the files with:
gcc vocTrainer.c german_menue.c english_menue.c -o v.exe
But I get an error of multiple definition even though I only include one of the language files depending on your input.
Multiple defintion of 'orderOfVoc'
First defined here: collect2.exe error: ld returned 1 exit status
My code:
vocTrainer.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "german_menue.h"
#include "english_menue.h"
int main(void)
{
char selectLang[1]; //store 1 for English or 2 for German
system("cls"); //clear screen
memset(selectLang,0,1); //set all fields in the array to 0
while(selectLang[1] != 1 && selectLang[1] != 2)
{
//select your language
printf("Choose language - Sprache auswaehlen:\n(1) - Englisch/English\n(2) - Deutsch/German\n");
scanf("%d",&selectLang[1]);
system("cls");
}
//language query
if(selectLang[1] == 2)
{
#include "german_menue.c"
}
else
{
#include "english_menue.c"
}
printf("Test of select Order: %d",orderOfVoc());
return 0;
}
german_menue.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "german_menue.h"
int orderOfVoc()
{
char selectOrder[1]; /*store the choosen order of vocabulary.
1 for one after another 2 for a random sequence of words*/
printf("Wie sollen die Vokabeln abgefragt werden?\n(1) - Der Reihe nach\n(2) - Zufaellig\n");
scanf("%d",&selectOrder[1]);
return selectOrder[1];
}
english_menue.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "german_menue.h"
int orderOfVoc()
{
char selectOrder[1]; /*store the choosen order of vocabulary.
1 for one after another 2 for a random sequence of words*/
printf("How do you want to learn the vocabulary?\n(1) - Vocabulary in order\n(2) - Random order\n");
scanf("%d",&selectOrder[1]);
return selectOrder[1];
}
german_menue.h
#ifndef GERMAN_MENUE_H //include guards
#define GERMAN_MENUE_H
extern int orderOfVoc();
#endif //GERMAN_MENUE_H
english_menue.h
#ifndef ENGLISH_MENUE_H //include guards
#define ENGLISH_MENUE_H
extern int orderOfVoc();
#endif //ENGLISH_MENUE_H
Primary Issue: In your code,
if(selectLang[1] == 2)
{
#include "german_menue.c"
}
else
{
#include "english_menue.c"
}
is not doing what you're thinking. There are may issues, like
#include is compile time operation (during preprocessing state) and essentially cannot be controlled at runtime.
You don't include source files. You compile and link them together. Your compilation statement looks correct. Just leave out the above mentioned code snippet from your code.
Just to add a bit detail regarding the reason behind the error you received, is because, you have #includeed the source files (which is essentially adding the source code of that .c file in vocTrainer.c file itself) and again, at compile time, you're putting the .c files. Thus, after compilation, at linking state, compiler sees more than one occurrences of orderOfVoc() which is why compiler is complaining.
Solution:
You remove different definition of orderOfVoc() function. Make use of the user selected value. Pass the value to the orderOfVoc() as an argument, and execute accordingly.
Secondary Issue(s): Apart from above issue(s), in your code, with a definition like
char selectLang[1];
writing
scanf("%d",&selectLang[1]);
is wrong, because
selectLang[1] is out of bound access. Array index in C starts from 0.
%d is not the correct formart specifier for char.
FWIW, char selectLang[1]; is functionally equivalent with char selectLang;
A modified version (not tested) for aforesaid approach:
select_menue.h
#ifndef SELECT_MENUE_H //include guards
#define SELECT_MENUE_H
//according to {store 1 for English or 2 for German}
#define ENGLISH 1
#define GERMAN 2
extern int orderOfVoc(int);
#endif //SELECT_MENUE_H
select_menue.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "select_menue.h"
int orderOfVoc(int lang)
{
int selectOrder = 0;
switch (lang)
{
case ENGLISH:
printf("How do you want to learn the vocabulary?\n(1) - Vocabulary in order\n(2) - Random order\n");
scanf("%d",&selectOrder); //add possible error check
break;
case GERMAN:
printf("Wie sollen die Vokabeln abgefragt werden?\n(1) - Der Reihe nach\n(2) - Zufaellig\n");
scanf("%d",&selectOrder); //add possible error check
break;
}
return selectOrder;
}
vocTrainer.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "select_menu.h"
int main(void)
{
int selectLang = 0; //array not required, initialize in single statement
//store 1 for English or 2 for German
while(selectLang != 1 && selectLang != 2)
{
//select your language
printf("Choose language - Sprache auswaehlen:\n(1) - Englisch/English\n(2) - Deutsch/German\n");
scanf("%d",&selectLang);
}
printf("Test of select Order: %d",orderOfVoc(selectLang));
return 0;
}
#include is a preprocessor directive that includes the contents of the file named at compile time.
The code that conditionally includes stuff is executed at run time...not compile time. So both files are being compiled in. ( You're also including each file twice, once in the main function and once above it, which is just confusing and probably wrong, but we'll ignore that for now. )
You can't really conditionally include stuff at run time. You can use other preprocessor directives (#ifdef, etc. ) to conditionally include one or the other file at compile time, but for your purposes you really need to have some sort of global flag that each function in the included files uses to determine if it should display english or german, etc.
Internationalization of strings is a whole topic in itself. There are lots of ways to handle it, and some libraries to make it easier depending on your platform.
Here's one way you could handle the same scenari:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "german_menue.h"
char *getLocalizedString(int stringId)
{
// Pseudo-Code, not real C++
// Also ignores memory issues and deallocating strings when done
char *localizedString = LoadGermanOrEnglishStringBasedOnGlobalVarForLanguage(stringId);
return localizedString ;
}
int orderOfVoc()
{
int stringId = 1;//should be constant for this message
char *localizedString = getLocalizedString(stringId);
printf("%s", localizedString);
scanf("%d",&selectOrder[1]);
return selectOrder[1];
}
I'm doing a project for school, so I need to compile it with:
gcc hide.c stegano.c -o hide -ansi -pedantic -Wall -Werror
But then I get this errors:
/tmp/ccDME1jC.o: In function `calculate_n':
stegano.c:(.text+0x0): multiple definition of `calculate_n'
/tmp/ccQxPZJu.o:hide.c:(.text+0x0): first defined here
/tmp/ccDME1jC.o: In function `tam_msg':
stegano.c:(.text+0x87): multiple definition of `tam_msg'
/tmp/ccQxPZJu.o:hide.c:(.text+0x87): first defined here
/tmp/ccDME1jC.o: In function `insere_msg':
stegano.c:(.text+0xe1): multiple definition of `insere_msg'
/tmp/ccQxPZJu.o:hide.c:(.text+0xe1): first defined here
/tmp/ccDME1jC.o: In function `copia':
stegano.c:(.text+0x201): multiple definition of `copia'
/tmp/ccQxPZJu.o:hide.c:(.text+0x201): first defined here
/tmp/ccDME1jC.o: In function `esconde_msg':
stegano.c:(.text+0x274): multiple definition of `esconde_msg'
/tmp/ccQxPZJu.o:hide.c:(.text+0x274): first defined here
collect2: ld returned 1 exit status
The program code is like this, I think that the error is probably in the include's so I hid the actual code:
The program hide.c is like this:
#include <stdio.h>
#include <stdlib.h>
#include "stegano.c"
//code//
Then it calls stegano.c, that contains all the actual function used in hide.c:
#include <stdio.h>
#include <stdlib.h>
#include "stegano.h"
//code//
And the header file stegano.h:
#include <stdio.h>
#include <stdlib.h>
#define MAX 100
typedef unsigned char Byte;
void calculate_n(char name[MAX], int* n, int* x);
int tam_msg(char name[MAX]);
void insere_msg(int size, char name[MAX], Byte* v);
void copia(Byte* v1, Byte *v2, int size);
void esconde_msg(Byte* msg, char name1[MAX], char name2[MAX]);
Thanks for helping!
Caused by this:
#include "stegano.c"
this will pull all the function definitions in stegano.c into hide.c. Meaning the stegano.c and hide.c now define the same functions. This will produce the multiple definition errors you see when you attempt to (compile and) link.
Include the header file instead:
#include "stegano.h"
You need to remove the #include "stegano.c". Include the stegano.h file instead.
By including the .c file you basically try to compile the code from that file twice (once when including it and once when compiling the file directly) and thus both stegano.o and hide.o will contain the same functions which will break in the linking phase.