Define Linker Error
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Fatal Errors Logic Errors Note that the error messages shown below may be specific to our compiler/linker or machines. Nonetheless, other systems and linker error already defined in obj compilers will provide similar information. Compiler Messages When the compiler define linker histone is compiling your code (i.e., converting your code into instructions the machine understands), it will report problems define linker and loader that it finds in your code. Aside: Here, we are being technical and refer to compiling as the stage before linking. Linking is when all the compiled
Linker Error Undefined Reference To
pieces of a program and the libraries it uses (e.g., for cin) are put together to form an executable. Often, compiling and linking together are just referred to as compiling. There are two severities of messages the compiler can give: Compiler Warnings A compiler warning indicates you've done something bad, but not something that will linker error undefined symbols for architecture x86_64 prevent the code from being compiled. You should fix whatever causes warnings since they often lead to other problems that will not be so easy to find. Example: Your code calls the pow() (raise to a power) library function, but you forgot to include math.h. Because you've supplied no prototype for the pow() function (its in math.h), the compiler warns you that it assumes pow() returns an int and that it assumes nothing about pow()'s parameters: somefile.cpp:6: warning: implicit declaration of function `int pow(...)' This is a problem since pow() actually returns a double. In addition, the compiler can't type-check (and possibly convert) values passed to pow() if it doesn't know how many and what type those parameters are supposed to be. Note: The compiler will label warnings with the word warning so that you can distinguish them from errors. Compiler Errors A compiler error indicates something that must be fixed before the code can be compiled. Example: You forget a semi-colon
Fatal Errors Logic Errors Note that the error messages shown below may be specific to our compiler/linker or machines. Nonetheless, other systems and compilers will provide similar information. Compiler Messages When the compiler is compiling your linker error xcode code (i.e., converting your code into instructions the machine understands), it will report
Linker Error C++
problems that it finds in your code. Aside: Here, we are being technical and refer to compiling as the stage
Apple Mach-o Linker Error
before linking. Linking is when all the compiled pieces of a program and the libraries it uses (e.g., for cin) are put together to form an executable. Often, compiling and linking together are just https://www.cs.bu.edu/teaching/cpp/debugging/errors/ referred to as compiling. There are two severities of messages the compiler can give: Compiler Warnings A compiler warning indicates you've done something bad, but not something that will prevent the code from being compiled. You should fix whatever causes warnings since they often lead to other problems that will not be so easy to find. Example: Your code calls the pow() (raise to a power) library function, https://www.cs.bu.edu/teaching/cpp/debugging/errors/ but you forgot to include math.h. Because you've supplied no prototype for the pow() function (its in math.h), the compiler warns you that it assumes pow() returns an int and that it assumes nothing about pow()'s parameters: somefile.cpp:6: warning: implicit declaration of function `int pow(...)' This is a problem since pow() actually returns a double. In addition, the compiler can't type-check (and possibly convert) values passed to pow() if it doesn't know how many and what type those parameters are supposed to be. Note: The compiler will label warnings with the word warning so that you can distinguish them from errors. Compiler Errors A compiler error indicates something that must be fixed before the code can be compiled. Example: You forget a semi-colon (;) at the end of a statement and the compiler reports: somefile.cpp:24: parse error before `something' Always remember to fix the first few errors or warnings, since they may be causing all the rest. Compiler messages usually list the file and line number where a problem occurs. Nonetheless, errors often occur on the lines prior to what the error message lists. Especially check the line immediately preceding where the error message indicates. Finally, note that some compile
some background. What is the linker? Consider the framework of a typical C++ program shown below. The main program in main.cpp uses a class called Type1, declared in the file type1.h-no executable code appears here-and defined, http://inst.eecs.berkeley.edu/~selfpace/studyguide/9F.sg/Output/linker.errors.html with executable code, in the file type1.cpp. A private class variable in the Type1 class is an object of Type2, similarly declared in the file type2.h and defined in the file type2.cpp. main.cpp #include
C++ programmers sometimes spend lots of time trying to understand and repair compiler and linker errors. If you can't understand the message, you're stuck. With a compiler error, the problem is easier to diagnose because it is related to the compilation of one source code module and the header files it includes. The compiler generally tells you the exact location of any error that it detects. With a linker error, the problem is related to how your source code modules link together. When the linker stage is reached, all the individual modules have compiled without errors. Linker errors can be caused by bugs in C++ code, but they can also be a result of mistakes in the project file. Error: Unable to find libxxx.so.x For Win32 Users At compile-time, your IDE needs to find the .DLL. To remedy this situation, drill into your menu structure until you find project -> properties -> C/C++ build -> libraries. Here, you can add a 3rd party library, and you'll be asked in a dialog for the location of headers and DLL files. At runtime, your PATH system environment variable must contain the directory where the required DLLs are located. Installing a library means making it available for more than a single user on a system. It is also possible to reuse a library without installing it. All libraries that you reuse must either be installed or placed in a directory listed in your LD_LIBRARY_PATH. When you reuse a library for the first time, you will probably see this error message. It means that the linker can not find the library. When the gnu linker looks for a shared object, it checks at least two places: The directories specified in LD_LIBRARY_PATH Installed libraries referenced from a cache file called /etc/ld.so.cache The Cache File: ld.so.cache The cache file provides fast lookup of shared objects found in the directories specified in /etc/ld.so.conf. Some directories you might find there are /lib /usr/lib /usr/X11R6/lib /usr/i486-linuxlibc1/lib /usr/local/lib /usr/lib/mozilla If you use a Linux package installer to install a library, it probably makes the proper changes to ld.so.conf and rebuilds your cache file. However, if you manually compile and install libraries, it may be necessary for you to edit this file. Afterward, you can rebuild the cache file with the command: l