sorry if this has been asked over and over but i just don't get what's wrong with this C code, since it was compiling with no problems until someday it started complaining about "C2009: Initializer is not a constant" in lines 9 and 10 of this header:
// CONIO2.H
#ifndef CONIO2_H_INCLUDED
#define CONIO2_H_INCLUDED
#ifndef _WINDOWS_
#include <windows.h>
#endif
void clrscr(void) {
int Written = 0;
COORD ord;
ord.X = 0;
ord.Y = 0;
FillConsoleOutputCharacter(GetStdHandle(STD_OUTPUT_HANDLE), 32, 80 * 25, ord, &Written);
}
//MAIN.C
#include <stdio.h>
#include <conio2.h>
Edit: I found the error. I was using the Eclipse CDT plugin for developing C applications but it wasn't setting up the path correctly. I had to play with the configs to make it work, but thanks anyways!
COORD ord;
You are missing the definition of the COORD type alias. My guess is you are not including the right header: Wincon.h
See here for the requirements (the header to include) to use the COORD type alias:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms682119(v=vs.85).aspx
EDIT: moreover you seems to have an issue with your #ifndef directives: there are two #ifndef but only one #endif in your header. For each #ifndef you need an #endif. And are you sure you want to include windows.h only when _WINDOWS_ is not defined?
This link describes the error along-with some examples. It may help you. As per the link, the compiler initializes non-automatic variables at the start of the program and the values they are initialized with must be constant. http://msdn.microsoft.com/en-us/library/t801az8a(v=vs.80).aspx
Your code has several pre-processor oddities. The below code works well on a standard C compiler for Windows. Please note that VC++ is not a standard C compiler, so it could toss all kinds of strange errors at you.
// CONIO2.H
#ifndef CONIO2_H_INCLUDED
#define CONIO2_H_INCLUDED
#include <windows.h>
void clrscr (void)
{
DWORD Written = 0;
COORD ord;
ord.X = 0;
ord.Y = 0;
FillConsoleOutputCharacter (GetStdHandle(STD_OUTPUT_HANDLE),
32,
80 * 25,
ord,
&Written);
}
#endif /* CONIO2_H_INCLUDED */
//MAIN.C
#include <stdio.h>
#include "conio2.h"
Related
Using Qt Creator I made these plain C files just to test my understanding:
main.c
#include <stdio.h>
#include "linked.h"
int main()
{
printf("Hello World!\n");
printf("%d", linked());
return 0;
}
linked.h
#ifndef LINKED_H_
#define LINKED_H_
int linked(void);
#endif // LINKED_H
linked.c
int linked()
{
return 5;
}
The IDE shows a warning on the line of linked.h in-between #define LINKED_H_ and int linked(void); which reads
ISO C requires a translation unit to contain at least one declaration
My best guess about what this means is that any header or other C file, if it is in a project, should get used in the main file at least once somewhere. I've tried searching the warning but if this has been answered elsewhere, I'm not able to understand the answer. It seems to me I've used the linked function and so it shouldn't give me this warning. Can anyone explain what's going on?
The program compiles and runs exactly as expected.
I think the issue is that you don't #include "linked.h" from linked.c. The current linked.c file doesn't have any declarations; it only has one function definition.
To fix this, add this line to linked.c:
#include "linked.h"
I don't know why it says this is an issue with linked.h, but it seems to be quite a coincidence that the line number you pointed out just happens to be the line number of the end of linked.c.
Of course, that may be all this is; a coincidence. So, if that doesn't work, try putting some sort of external declaration in this file. The easiest way to do that is to include a standard header, such as stdio.h. I would still advise you to #include "linked.h" from inside linked.c, though.
add a header
#ifndef LINKED_H_
#define LINKED_H_
#include <stdio.h>
int linked(void);
#endif // LINKED_H
The way you wrote the code, you need to use:
extern int linked(void);
(notice the additional "extern"). That might help with the issue.
Also, the code in linked.c should be:
int linked(void)
{
return 5;
}
(Notice the "parameter" - "void").
According to IBM, you need some declaration in the header file, but you do have one. Perhaps LINKED_H_ is defined elsewhere, or the compiler is seeing that it's possible that the precompiler condition might result in an empty parse.
Perhaps this header file will work for you:
linked.h
#ifndef LINKED_H_
#define LINKED_H_
int linked(void);
#endif // LINKED_H
char __allowLinkedHToBeIsoCCompliant = 1;
In the following code, it is compiled success and print 1024
#include <stdio.h>
#define FD_SETSIZE 512
#include <sys/types.h>
int main()
{
printf("%d\n", FD_SETSIZE);
}
But in the following code, it is compiled failed and print
test.c:4:1: warning: "FD_SETSIZE" redefined
In file included from /usr/include/sys/types.h:220,
from test_fd.c:3:
/usr/include/sys/select.h:81:1: warning: this is the location of the previous definition
the code is
#include <stdio.h>
#include <sys/types.h>
#define FD_SETSIZE 512
int main()
{
printf("%d\n", FD_SETSIZE);
}
Can anbody explain this? Thanks!
But in the following code, it is compiled failed and print
In the question, both the programs were compiled, but while compiling first program you got warnings in preprocessor stage.
Preprocessor stage is responsible for the replacement of macros.
In this example the preprocessor is using the last defined macro and replacing it.
#include <stdio.h>
#define FD_SETSIZE 512
#include <sys/types.h>
Here the definition of FD_SETSIZE is there in both the .c file and also in header file sys/types.h.
After the file inclusion, then the replacing of macros will be done,so the latest defined macro is replaced.
So the final replacement FD_SETSIZE of will be same as defined in the sys/types.h file and vice-versa.
Hope this is helpful.
you can use the #undef directive to remove the defined macro and replace it later
#ifdef MACRO
#undef MACRO
#endif
#define MACRO
I have a weird problem with my C-Code that I don't really understand.
I have two header files os_memory.h and os_mem_drivers.h.
os_memory.h
#ifndef OS_MEMORY_H_
#define OS_MEMORY_H_
#include "lcd.h"
#include "os_mem_drivers.h"
static const MemAddr gui_alloc_table_start = 0x1C8;
#endif /* OS_MEMORY_H_ */
os_mem_drivers.h
#ifndef OS_MEM_DRIVERS_H_
#define OS_MEM_DRIVERS_H_
#include "os_memory.h"
#include "defines.h"
#include "os_core.h"
typedef uint16_t MemAddr;
#endif
If I try to compile this code the compiler gives me the error unknown type name 'MemAddr'. I don't get it because I included the right header files in each .h file so there shouldn't be any error.
Is there anything that I'm missing here?
I'm using AtmelStudio 6.1 and the C language for this project.
You should move the definition for type MemAddr before including "os_memory.h":
os_mem_drivers.h:
#ifndef OS_MEM_DRIVERS_H_
#define OS_MEM_DRIVERS_H_
#include <stdint.h>
typedef uint16_t MemAddr;
#include "os_memory.h"
#include "defines.h"
#include "os_core.h"
#endif
But a more important problem is the circular inclusion of "os_memory.h" and "os_mem_drivers.h". Each one includes the other: include guards prevent recursive inclusion but make it difficult to understand what is really going on. You should try and fix this issue.
I want to define a constant depending on the OS in use.
As such:
#include <stdio.h>
#ifdef _Win32 //Used for system("cls") command
#include <process.h>
#define CLEAR "system(\"cls\")"
#endif
#ifdef __APPLE__
#define CLEAR "system(\"clear\")"
#endif
int main()
{
CLEAR;
}
Xcode gives me an error stating that expression result unused at
#define CLEAR "system(\"clear\") and inside the main function.
I am on a Mac.
Use:
#define CLEAR system("clear")
not
#define CLEAR "system(\"clear\")"
You get the error because your macro call is substituted with:
"system(\"clear\")";
which is a useless expression statement (the expression being the string here) like for example:
0; // valid but pointless
try altering your main function as such:
int main()
{
int rc;
rc = CLEAR;
return rc;
}
You need to catch the return value of the system() call and use it
#define CLEAR system("clear")
and not
#define CLEAR "system(\"clear\")"
The compiler will create a new C code (called pre-processor code) in which will replace the macro name by its content.
so if you define macro in this way:
#define CLEAR "system(\"clear\")"
You will get in the new code (pre-processor code) generated by the Compiler:
int main()
{
"system(\"clear\")";
}
You can see the code generated by the compiler (pre-processor code) with gcc -E
I'm just getting started with modular programming in C. I think I'm doing something wrong with the inclusions, because I'm getting a lot of conflicting types for 'functionName' and previous declaration of 'functionName' was here errors. I did put inclusion guards in place.
Do you know a clear tutorial that explains modular programming in C, especially how the inclusions work?
Update: I have tried to isolate my issue. Here's some code, as requested.
Update 2: updated code is below. The errors have been updated, too.
/*
* main.c
*/
#include <stdio.h>
#include "aStruct.h"
int main() {
aStruct asTest = createStruct();
return 0;
}
/*
* aStruct.h
*/
#ifndef ASTRUCT_H_
#define ASTRUCT_H_
struct aStruct {
int value1;
int value2;
struct smallerStruct ssTest;
};
typedef struct aStruct aStruct;
aStruct createStruct();
#endif /* ASTRUCT_H_ */
/*
* smallerStruct.h
*/
#ifndef SMALLERSTRUCT_H_
#define SMALLERSTRUCT_H_
struct smallerStruct {
int value3;
};
typedef struct smallerStruct smallerStruct;
smallerStruct createSmallerStruct();
#endif /* SMALLERSTRUCT_H_ */
/*
* aStruct.c
*/
#include <stdio.h>
#include "smallerStruct.h"
#include "aStruct.h"
aStruct createStruct() {
aStruct asOutput;
printf("This makes sure that this code depends on stdio.h, just to make sure I know where the inclusion directive should go (main.c or aStruct.c).\n");
asOutput.value1 = 5;
asOutput.value2 = 5;
asOutput.ssTest = createSmallerStruct();
return asOutput;
}
/*
* smallerStruct.c
*/
#include <stdio.h>
#include "smallerStruct.h"
smallerStruct createSmallerStruct() {
smallerStruct ssOutput;
ssOutput.value3 = 41;
return ssOutput;
}
This generates the following error messages:
At aStruct.h:10
field 'ssTest' has incomplete type
At main.c:8
unused variable `asTest' (this one makes sense)
The base of inclusion is to make sure that your headers are included only once. This is usually performed with a sequence like this one:
/* header.h */
#ifndef header_h_
#define header_h_
/* Your code here ... */
#endif /* header_h_ */
The second point is to take care of possible name conflicts by handling manually pseudo namespaces with prefixes.
Then put in your headers only function declarations of public API. This may imply to add typedefs and enums. Avoid as much as possible to include constant and variable declarations: prefer accessor functions.
Another rule is to never include .c files, only .h. This is the very point of modularity: a given module dependant of another module needs only to know its interface, not its implementation.
A for your specific problem, aStruct.h uses struct smallerStruct but knows nothing about it, in particular its size for being able to allocate an aStruct variable. aStruct.h needs to include smallerStruct.h. Including smallerStruct.h before aStruct.h in main.c doesn't solve the issue when compiling aStruct.c.
The multiple definition problem is most likely coming from the way you're including the code. You are using #include "aStruct.c" as opposed to #include "aStruct.h". I suspect you are also compiling the .c files into your project in addition to the #include. This causes the compiler to become confused due to the multiple definitions of the same function.
If you change the #include to #include "aStruct.h" and make sure the three source files are compiled and linked together, the error should go away.
Such errors mean that function declaration (return type or parameter count/types) differs from other function declarations or function definition.
previous declaration message points you to the conflicting declaration.