I am trying to compile my C program in Ubuntu 9.10 (gcc 4.4.1).
I am getting this error:
Rect.cpp:344: error: ‘memset’ was not declared in this scope
But the problem is I have already included in my cpp file:
#include <stdio.h>
#include <stdlib.h>
And the same program compiles fine under Ubuntu 8.04 (gcc 4.2.4).
Please tell me what am I missing.
You should include <string.h> (or its C++ equivalent, <cstring>).
Whevever you get a problem like this just go to the man page for the function in question and it will tell you what header you are missing, e.g.
$ man memset
MEMSET(3) BSD Library Functions Manual MEMSET(3)
NAME
memset -- fill a byte string with a byte value
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <string.h>
void *
memset(void *b, int c, size_t len);
Note that for C++ it's generally preferable to use the proper equivalent C++ headers, <cstring>/<cstdio>/<cstdlib>/etc, rather than C's <string.h>/<stdio.h>/<stdlib.h>/etc.
Related
I've set up a cross compiler for my raspberry pi, the one I found here: Installing Raspberry Pi Cross-Compiler
Now this has been working fine, up to the point where I want to use an I2c library (i2c-dev.h).
When compiling the code below with the arm-linux-gnueabihf-g++ compiler, I get an error:
In file included from src/I2c.cpp:8:0:
src/../Include/I2c.h:29:18: error: field ‘message’ has incomplete type
struct i2c_msg message;
^
Meanwhile, when I compile the code on a raspi, it simply runs.
#ifndef I2C_H_
#define I2C_H_
#include <linux/i2c-dev.h> // Defines i2c_msg
#include ...
using namespace std;
typedef struct {
struct i2c_msg message;
void (*callback)(int);
int messageID;
} t_msgQueue;
Any ideas on a possible cause, or a solution on how I can make the cross compiler work properly?
My first suspect would be differing GCC versions between the RPi and your cross compiler; GCC has been known to change how it processes #include statements over time.
Barring a version difference, check to ensure that a host include file hasn't been picked up somwhere by accident.
Problem was solved by adding a
#include <linux/i2c.h>
before the i2c-dev headers. Still no idea why the two compilers gave different results...
I was using CImg for picture processing, which don't compile for C++11 or above:
CImg.h:48902:22: error: there are no arguments to 'pclose' that depend on a template parameter, so a declaration of 'pclose' must be available [-fpermissive]
But my program which includes CImg.h does use some C++11 feature. Can I use different C++ standard to process these two files? CImg.h itself is a header+code so I have to #include that.
Here is my test program:
#define cimg_display 0
#include "CImg.h"
int main(){}
CImg.h comes from the lastest version from http://cimg.eu/.
I'm very new in Ubuntu and programming C++ on Ubuntu using Geany.
The problem I have here is that:
the classes i want to iclude to my project will receive an error,
I type,
#include <vector>
the error given here is,
fatal error: vector: No such file or directory
also I cannot use namespace std,
typing using namespace std returns the following error,
error: unknown type name 'using'
Here is the code:
#include <stdio.h> //no problem here
#include "stdlib.h" //no problem here
#include <vector> //this is a problem (lets say it returns error 1)
using namespace std; //this is a problem (lets say it returns error 2)
int main(int argc, char **argv)
{
return 0;
}
This sounds like you are using the wrong compiler to compile your C++ code. For example, by invoking gcc test.cpp the C++ file is actually compiled as C and you receive errors such as the one you posted - there is no vector header in C and there is also no using keyword.
If you are using gcc, the correct way to invoke the compiler to compile C++ is via the g++ symlink, i.e. g++ test.cpp
If you are using clang, the executable is called clang++ instead.
Both compilers support the -x parameter to manually change the language to C++, although in that case you also have to specify that the compiler needs to link your files with the C++ standard library. For example: gcc -x c++ test.cpp -lstdc++
Where or how can I find the correct C headers to include in a C++ program to obtain the declaration of C functions declared in a POSIX compliant environment?
I'm asking this because I needed to use the open() system call in my C++ program for my purposes, so I initially tried to include the headers mentioned in the online documentation about open() (in the SYNOPSIS section), which are sys/stat.h and fcntl.h. However when trying to compile, the compiler complained that open() was not declared. After a search on google, I found that another possibility was unistd.h. I tried using that header and the program compiled. So I went back to the POSIX documentation to read more about unistd.h to check if open() was mentioned there, but I could not find anything about it.
What am I doing wrong? Why is there this discrepancy between the POSIX documentation and my GCC environment?
On my Linux Debian/Sid, the man 2 open page states:
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
So you need to include all three above files. And open is declared in /usr/include/fcntl.h but needs declaration from the other two includes.
And the following test file
/* file testopen.c */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int
testopen (void)
{
return open ("/dev/null", O_RDONLY);
}
compiles with gcc -Wall -c testopen.c without any warnings.
I have the following source code. Which compiles fine in visual studios and g++ 3.4.6; but not with g++ 4.4.3 (on a newer ubuntu machine). The newer compiler requires that I explicitly include to use atoi. I am just trying to figure out what might have changed to cause this behavior. Is it sstream header file previously included cstdlib and no longer does so. Or is it the compiler behavior that has changed.
#include <sstream>
int main()
{
char str1[]="123";
int i = atoi(str1);
printf ("value = %d",i);
return 0;
}
You also need to include <cstdio> for printf().
Technically, if you include the headers of the form <cname> instead of <name.h>, you also need to qualify the names from the standard library using std::. A lot of standard library implementations are relaxed when it comes to this, though, and also put the names into the global namespace.
It's implementation-dependent which headers are included by which other headers, so you should always be sure to include all the headers that you need and not assume that they will be included automatically.
I'm using GCC 4.4.5 on Debian, and the headers have changed so you will not bring in the headers necessary. You need to #include <cstdlib> and #include <cstdio> to get atoi and printf, as the compiler complained about both being missing.
#include <sstream>
#include <cstdio>
#include <cstdlib>
int main()
{
char str1[]="123";
int i = std::atoi(str1);
std::printf ("value = %d",i);
return 0;
}
Well yes. That is common. You should always include ALL headers that you are directly using and not depend on the fact that those headers are already included.
Compiler behavior is what would have changed... the <sstream> doesn't use atoi.
Arguably you should have always done #include <cstdlib>, and you'd gotten lucky with your previous compilers.
As James McNeillis points out, you should also #include <cstdio> in order to use the printf function.