C++ error: expected primary-expression before ‘[’ token

Question

Now I'm trying to install RealPlexor by dklab, but it's falls with errors:

# bash ./Make.sh 
In file included from dklab_realplexor.cpp:68:
utils/misc.h: In function ‘void die(std::string)’:
utils/misc.h:105: error: expected primary-expression before ‘[’ token
compilation terminated due to -Wfatal-errors.

Here is that line

s = regex_replace(s, regex("\\$!"), [](smatch s) { return strerrno(); });

• DavidO: What's the line preceding this one?
• WhozCraig: Your certain your toolchain is (a) compiling with c++11 compliance and (b) supports lamdas ?
• Kirill Danshin: @DavidO void die(string s) { s = regex_replace(s, regex("\\$!"), *(smatch s) { return strerrno(); }); throw runtime_error(s); }
• Kirill Danshin: @WhozCraig my server is running on Debian with gcc (Debian 4.4.5-8) 4.4.5
• WhozCraig: I suspected so. Lambda expression support was not added to g++ until 4.5. Read this, or this.

Answer 1

Make sure that you are passing the following flag to your compiler (as described in the the g++ documentation):

-std=c++11

This tells the gcc compiler (g++) to compile your code with C++11 semantics.

The lambda expression syntax you are using (the part starting with []) is a C++11 feature, and will cause compilers great confusion if it appears in code that they aren't expecting to be C++11.

However, as has been pointed out in another comment here (and is confirmed by this table, the version of gcc you are running (4.4.5, per a comment) doesn't have lambda expression support. May have to use a function object instead, or upgrade to a newer version of gcc/g++.

• Kirill Danshin: Don't work, falls with # bash ./Make.sh In file included from dklab_realplexor.cpp:68:0: utils/misc.h: In function ‘void die(std::string)’: utils/misc.h:105:50: error: expected primary-expression before ‘s’ compilation terminated due to -Wfatal-errors.
• DavidO: If you're still experiencing the error after upgrading g++ to 4.7, then you're not using the -std=c++11 flag as documented in gcc.gnu.org/onlinedocs/gcc/Standards.html , and judging from some of your other comments, I would say you probably need to set Make.sh to generate the appropriate flags in the project's makefile.
• DavidO: For example, create the simplest C++11 program you can, that uses some simple C++11 feature. Compile it with g++ -std=c++11 mytest.cpp -o mytest, and you can confirm for yourself in a simpler environment that the compiler flag works.

Answer 2

Just say

s = regex_replace(s, regex("\\$!"), *(smatch s) { return strerrno(); });

The [] operator is usually used to index something (like a character array), so C++ expects something in front of it

Also try this suggestion from @DavidO:

You're using a lambda expression which is a C++11 syntax, but probably haven't set your compiler to recognize C++11. If you're using g++, you would use the -std=c++11 flag.

• Kirill Danshin: now its falls with # bash ./Make.sh In file included from dklab_realplexor.cpp:68: utils/misc.h: In function ‘void die(std::string)’: utils/misc.h:105: error: expected primary-expression before ‘s’ compilation terminated due to -Wfatal-errors.
• Dietmar Kühl: Is using *(smatch s){ return strerrno(); } a new way to specify lambdas in C++?
• Lawrence Aiello: I am not sure, I have never used C++11
• DavidO: There you go; you're using a lambda expression which is a C++11 syntax, but probably haven't set your compiler to recognize C++11. If you're using g++, you would use the -std=c++11 flag.
• Lawrence Aiello: I'll add that in my answer