This question already has answers here:
Undefined reference to `sin` [duplicate]
(4 answers)
Closed 9 years ago.
I have include the math.h in my c file, however it keeps prompts undefined reference to truncand undefined reference to ceil. And I didn't even use trunc in my file. Could anyone tell what was the problem?
If you compile using gcc, you might need to add -lm option to link to the math library (libm) like
gcc test.c -lm
It seems that you will need the info about how C source code are compiled and linked together.
The link contains some basic info:
Compile & Link
You use -I option of gcc to specify where to find headers, and -l option to link standard libraries
Related
This question already has answers here:
Why do you have to link the math library in C?
(14 answers)
Closed 4 years ago.
I could not found any documentation on why gcc requires -lm for math.h functions but no -l is required for stdio or stdlib functions. Why some functions require the include and the -l gcc command option, and others don't require the -l option? Any thoughts?
There are some libraries which gets linked by default.
One of those default libraries for gcc is libc.a (static) or libc.so (dynamic) (GNU standard C library), and it contains the definition of printf() and scanf() families, including others, prototyped in stdio.h or stdlib.h .
Now, to answer your question, according to the wikipedia article
Under FreeBSD and Linux,[8] the mathematical functions (as declared in math.h) are bundled separately in the mathematical library libm. If any of them are used, the linker must be given the directive -lm.
If you want to check explicitly about the libraries getting linked by deafult, you need to use -v option to check them. You can also pass -Wl,--verbose option to get even more verbose output.
If you want to restrict the default linking, you can make use of -nostdlib switch.
This question already has answers here:
CMake link to external library
(6 answers)
Closed 4 years ago.
I have a libname.a static library that works fine when I use gcc:
gcc -c main.c -o main.o ;
gcc main.o libname.a main
But now I would like to use CMake as the project is getting big, but I got this message and and I don't know how to include it in an appropriate way. (I tried link_target_library and/or link_directories and/or set(CMAKE_CC_FLAGS "absolute_path/libname.a").
Note that I don't have any source code for libname.a.
/usr/bin/ld: cannot find -llibname
As said in my comment target_link_libraries(${PROJECT_NAME} ${CMAKE_SOURCE_DIR}/libname.a) works. I can't really tell what the reason for your problem is (maybe you used target_link_library instead of target_link_libraries ?).
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Linker order - GCC
GCC C++ Linker errors: Undefined reference to 'vtable for XXX', Undefined reference to 'ClassName::ClassName()'
I am using GCC to build an application. The main program calls a function (say, myfunc())that resides in a static library (say, libmylib.a). This function calls the cosf() and sinf() function from math library.
Now, in gcc command line, I give the -lmylib -lm options, and the build goes fine. However, when the order of the libraries is changed, then the build fails with the error:
libmylib.a(mylib.o): In function `myfunc':
mylib.c:22: undefined reference to `cosf'
mylib.c:23: undefined reference to `sinf'
Why doesn't gcc complete the build with the libraries given in some order?
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Using GCC to produce readable assembly?
For example, when I try:
gcc -c myprogram
it will give me an object file, which is in binary form. What I would like to get is just an assembly file (right before it is processed by an assembler to produce the object file). Is there a way to do it in gcc?
just write gcc -S file.c, and you will get file.s which is assembly.
Yes. It's -S. See the manual.
This question already has answers here:
Closed 12 years ago.
Possible Duplicate:
Why Am I Getting Link Errors When Calling Function in Math.h?
Hello, I have a problem in C (gcc), when I compile a program that includes Math.h and uses functions from there, it says "undefined reference to...". it happens for sqrt, log, but for others not (for instance pow). How can I fix this library or reinstall it ? thanks in advance.
[I am using Ubuntu]
You shold link with -lm option: gcc -o test test.c -lm lm means link math.