gcc isn't finding iostream.h

[radfaraf]

I'm trying to compile some of my C++ programs for class on linux, but gcc isn't finding iostream.h

gcc -c array.c array
gcc: array: No such file or directory
array.c:2: iostream.h: No such file or directory

The file is at
/usr/lib/gcc-lib/i686-pc-linux-gnu/2.95.3/include/g++/iostream.h
but for some reason it's not finding it

[BlockFin]

I'm not sure why this is happening, but as a temp fix, since you know the absolute path you can #include that.

Also, #include <g++/iostream.h> might work.

[trythil]

Well, to be C++ Standard-conformant, you should be using <iostream> instead of <iostream.h>...but I digress. 2.95.3 fakes understanding of <iostream> (and for that matter a lot of C++) anyway

C++ includes are usually found in /usr/include/g++. On my system, which is using GCC 3.1, they're in /usr/include/g++-v31/. Look for anything similar in your /usr/include directory -- if nothing is there, you will have to symlink.

Alternatively, you could change your compiler options to:

g++ -I/usr/lib/gcc-lib/i686-pc-linux-gnu/2.95.3/include/g++ array.c array

By the way, you don't want to use -c here, if array is a stand-alone program. -c tells the compiler to generate an object file only and skip the linking process.

[TwoSlick]

I'm having the exact same problem, but I think that gcc is finding the iostream.h file. It's just screwing up in some other way. I tried including the entire path to the file, and still get the same error

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gcc test.cpp

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/tmp/ccgxpCGn.o: In function `main':
/tmp/ccgxpCGn.o(.text+0xc): undefined reference to `cout'
/tmp/ccgxpCGn.o(.text+0x11): undefined reference to `ostream::operator<<(int)'
collect2: ld returned 1 exit status

However if I use:

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g++ test.cpp

The problems are gone.

Weird
-Tim

[rac]

Things like "undefined refence to cout" are often a result of failure to link with the standard C++ library, by adding -lstdc++ to the link command. It's hard to say more without seeing the contents of test.cpp.

Invoking gcc as g++ should not act any differently if called on a file with a recognizable C++ suffix. Is it possible that your "gcc" and "g++" are from different versions of GCC, one of which is broken?

[trythil]

Actually, that's the expected behavior -- g++ simply invokes gcc in, for lack of a better phrase, C++ mode. This involves, among other things, automatically linking libstdc++.

Using "gcc" by itself on a C++ source file will not work. Sometimes it's easy to recognize when you've made this mistake, sometimes it's not. GCC 3.1, in particular, likes to make a mess of the output:

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trythil@lothlann trythil $ g++ --version
g++ (GCC) 3.1
Copyright (C) 2002 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

trythil@lothlann trythil $ gcc test2.cpp
/tmp/cc3t45ew.o: In function `main':
/tmp/cc3t45ew.o(.text+0x18): undefined reference to `std::allocator<char>::allocator[in-charge]()'
/tmp/cc3t45ew.o(.text+0x32): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string[in-charge](char const*, std::allocator<char> const&)'
/tmp/cc3t45ew.o(.text+0x45): undefined reference to `std::allocator<char>::~allocator [in-charge]()'
/tmp/cc3t45ew.o(.text+0x5e): undefined reference to `std::allocator<char>::~allocator [in-charge]()'
/tmp/cc3t45ew.o(.text+0x85): undefined reference to `operator new(unsigned)'
/tmp/cc3t45ew.o(.text+0x97): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string[in-charge]()'
/tmp/cc3t45ew.o(.text+0xbd): undefined reference to `operator delete(void*)'
/tmp/cc3t45ew.o(.text+0xd6): undefined reference to `operator delete(void*)'
/tmp/cc3t45ew.o(.text+0xe8): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator=(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/tmp/cc3t45ew.o(.text+0xff): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string [in-charge]()'
/tmp/cc3t45ew.o(.text+0x10a): undefined reference to `operator delete(void*)'
/tmp/cc3t45ew.o(.text+0x125): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string [in-charge]()'
/tmp/cc3t45ew.o(.text+0x13e): undefined reference to `std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string [in-charge]()'
/tmp/cc3t45ew.o(.eh_frame+0x12): undefined reference to `__gxx_personality_v0'

trythil@lothlann trythil $ cat test2.cpp
#include <string>

using namespace std;
	
int main()
{
        string b("This is a test string.  This is only a test.");
        unsigned int i;
        unsigned int limit = 1000000;

        string *c;

        for(i = 0; i <= limit; i++)
        {
                c = new string(b);
                delete c;
        }
}

If you don't know what to look for, that can be a mess.
-digression-
Actually, that rule is applicable to pretty much ANY C++ compiler errors. Templates, in particular, generate really, really disgusting compiler errors, and if you try reading over the entire error you'll just go nuts. Far better to glance at it, figure out where the problem is, and fix it.
-end digression-


Using g++ or adding -lstdc++ will link this correctly.

BTW, that above file was part of a small benchmark I set up to determine relative speeds of string copying and deletion in C++ and C. Results surprised me -- C++ was faster.

[rac]

Using "gcc" by itself on a C++ source file will not work.

From http://gcc.gnu.org/onlinedocs/gcc-3.1/g ... king%20G++:

C++ source files conventionally use one of the suffixes .C, .cc, .cpp, .c++, .cp, or .cxx; preprocessed C++ files use the suffix .ii. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name gcc).

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rac@emma$ cat afo.cp
#include <iostream>

using std::cout;
using std::endl;

int main( int argc, char ** argv ) {
	cout << "hello world" << endl;

}

rac@emma$ gcc -o afo -lstdc++ afo.cp
rac@emma$ ./afo
hello world

Works for me; perhaps I'm misunderstanding you.

[trythil]

Using g++ or adding -lstdc++ will link this correctly.

It's possible to use gcc to compile and link C++ code. I just don't see the point in doing

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gcc -lstdc++ ...

when

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g++ ...

works just as well.