Why prev of iterator does work on via mac gcc

[Cheney Chen]

I tried to use prev for map after checking out
http://www.cplusplus.com/reference/iterator/prev/

But there's one error "test2.cpp:13: error: ‘prev’ was not declared in this scope
"

Here's my code

#include <iostream>
#include <set>
#include <map>
#include <typeinfo>
#include <iterator>
#include <algorithm> 
using namespace std;

int main() {
    map<int, int> testMap;
    testMap.insert(make_pair(1,1));
    testMap.insert(make_pair(2,1));
    for (map<int,int>::iterator it = testMap.begin(); it != prev(testMap.end()); it++) {
        cout<<"("<<it->first<<","<<it->second<<")"<<"\t";
    }
    
}

and gcc version:
gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)

Could someone help me out why's that, looks like prev is not defined in this gcc version here?

[Catfish666]

That's an old version of GCC (current version is 4.8.2).

std::prev() is a feature of C++11 (the C++ standard of 2011).
Your compiler, being too old, does not implement it.

I realize this is an un-solution, but if you don't need to use std::prev() then don't use it.
Your for() loop leaves out the last element in the map, is this really what you want?

Otherwise upgrade your compiler to a more recent version.

[Cheney Chen]

Thank you Catfish for the quick reply.
Yes, this is what I want, actually I just want to have an example for "prev".

Btw, could you furthermore point out how can we know it's "a feature of C++11" and which gcc version has it?

[Catfish666]

Features of C++11 are marked in the documentation.
See again the page for std::prev() and look for the C++11 Warning icon.
(Little C++11 icons appear in the menu on the left as well, where needed.)

http://www.cplusplus.com/reference/iterator/prev/

An alternative Wiki-style C++ reference that also marks C++11 features is:
http://en.cppreference.com/w/

As for C++11 support in GNU GCC:
http://gcc.gnu.org/projects/cxx0x.html

If you're using MacOS, perhaps you should look into Clang:
http://clang.llvm.org/cxx_status.html

[Cheney Chen]

Thank you Catfish, so helpful.

[Cheney Chen]

Today I tried with latest gcc but still no luck...

test3.cpp: In function ‘int main()’:
test3.cpp:13:79: error: ‘prev’ was not declared in this scope
for (map<int,int>::iterator it = testMap.begin(); it != prev(testMap.end()); it++) {
^
risestoke-lm:CppCheney qili$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-apple-darwin12.4.0/4.9.0/lto-wrapper
Target: x86_64-apple-darwin12.4.0
Configured with: ../gcc-4.9-20130811/configure --enable-languages=fortran,c++
Thread model: posix
gcc version 4.9.0 20130811 (experimental) (GCC)

More idea?

[Catfish666]

As far as I know, the default standard of GCC is usually C++98.
You can enforce a standard by using the -std command line flag.

$ g++ -std=c++98 test3.cpp -o test3_cpp98
$ g++ -std=c++11 test3.cpp -o test3_cpp11

And since we're here, it's good practice to extend warnings:

$ g++ -Wall -Wextra -Wpedantic -std=c++11 test3.cpp -o test3

[Cheney Chen]

Thank you Catfish,
It's insightful, from "man gcc", confirmed what you mentioned.

           gnu++03
               GNU dialect of -std=c++98.  This is the default for C++ code.