What is g++ -I option (capital i)? - g++

Question

Trying to do this and stumbled upon the -I option here: $ g++ -o version version.cpp -I/usr/local/qt4/include/QtCore -I/usr/local/qt4/include -L/usr/local/qt4/lib -lQtCore
I can't find any information about it

Answer 1

If you're looking for what -I does:
-I[/path/to/header-files]
Add search path to header files (.h) or (.hpp).
From https://caiorss.github.io/C-Cpp-Notes/compiler-flags-options.html
This pretty much just means that any #include statements you make to an external library (in your case qt) have to be referenced so that g++ knows where to look.

Answer 2

if my understanding is correct, question is about -i, not -L, I hope this helps:
-Idir Append directory dir to the list of directories searched for include files.
on this link
http://www.cs.virginia.edu/helpnet/Software_Development/compilers/g.html
g++ - GNU project C++ Compiler (v2 preliminary)
g++ [option | filename] ...
Capabilities
The C and C++ compilers are integrated. Both process input files through one or more of four stages: preprocessing, compilation, assembly, and linking.
C++ source files use one of the suffixes `.C', `.cc', or `.cxx'.
Options
There are many command-line options, including options to control details of optimization, warnings, and code generation, which are common to both gcc and g++. For full information on all options, see gcc(1).
Options must be separate: -dr' is quite different from- d -r '.
-c Compile or assemble the source files, but do not link. The compiler output is an object file corresponding to each source file.
-Dmacro Define macro macro with the string `1' as its definition.
-Dmacro=defn Define macro as defn
-E Stop after the preprocessing stage; do not run the compiler proper. The output is preprocessed source code, which is sent to the standard output.
- g Produce debugging information in the operating system's native format (for DBX or SDB or DWARF). GDB also can work with this debugging information. On most systems that use DBX format, `-g' enables use of extra debugging information that only GDB can use.
Unlike most other C compilers, GNU CC allows you to use ` -g' with `-O'. The shortcuts taken by optimized code may occasionally produce surprising results: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values were already at hand; some statements may execute in different places because they were moved out of loops.
Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs.
-Idir Append directory dir to the list of directories searched for include files.
-llibrary Use the library named library when linking. (C++ programs often require `-lg++' for successful linking.)
-O Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function.
Without `-O', the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you would expect from the source code.
Without `-O', only variables declared register are allocated in registers. The resulting compiled code is a little worse than produced by PCC without `-O'.
With `-O', the compiler tries to reduce code size and execution time.
-o file Place output in file file.