Recently, I had question posed to from a reader from Norway. He was working his way through my book and found that one of the programs wouldn’t compile on his Linux computer. The problem was that the C language math library isn’t automatically linked. The effect is that a linker error appears upon compiling.
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\nWeird thing: I get the same error on my Linux laptop. It was completely unexpected!<\/p>\n
Here is sample code, which comes from a blog post on June 18, 2016<\/a>:<\/p>\n I compiled at the command prompt using the following command:<\/p>\n The Ugh.<\/p>\n The clang<\/em> program is both a compiler and linker. The source code is compiled into object code and, upon success, linked into a program file. Clang then removes the object code file, Back in the old days, two programs handled the process, cc<\/em> and ld<\/em>, the compiler and linker, respectively. Today, both clang<\/em> and gcc<\/em> (and cc<\/em>) automatically call the ld<\/em> program, the linker, to complete the task. That’s when the error happens because the pow()<\/em> function lacks a definition — at least in the Linux computer’s standard C library.<\/p>\n On both the PC and the Mac, the math library is included in the standard C library — at least it appears so. Otherwise, the compiler automatically calls in the library. But in Linux, apparently, you must manually specify that the linker include the math library.<\/p>\n But isn’t the math library included with No!<\/p>\n If I comment out the The solution is to use the Libraries are typically stored in the And the program finally compiles and links.<\/p>\n In next week’s Lesson<\/a> I explore the process of adding a library in Code::Blocks, which is actually far more involved than using a command line switch, even if that’s what Code::Blocks does internally.<\/p>\n","protected":false},"excerpt":{"rendered":" Apparently some Linux releases don’t automatically compile some C Library math functions. Continue reading \r\n#include <stdio.h>\r\n#include <math.h>\r\n\r\nint main()\r\n{\r\n double t;\r\n\r\n for(t=1.0;t<=10.0;t++)\r\n printf(\"2 to the %.f power is %.f\\n\",\r\n t,\r\n pow(2.0,t));\r\n\r\n return(0);\r\n}<\/pre>\nclang -Wall 0618.c<\/code><\/pre>\n-Wall<\/code> switch displays all errors, which is the default in Code::Blocks. Here’s the compiler output:<\/p>\n\/tmp\/0618-e49f59.o: In function 'main':\r\n0618.c(.text+0x4d): undefined reference to `pow'\r\nclang; error: linker command failed with exit code 1 (use -v to see invocation)<\/code><\/pre>\n0618.o<\/code> in this example.<\/p>\n#include <math.h><\/code><\/em><\/p>\n#include<\/code> directive, you get a compiler warning. Clang recommends that you include the math.h<\/code> header file (which is one reason that I like and recommend that compiler), but you still see the linker error and the program doesn’t compile.<\/p>\n-lx<\/code> switch to direct clang<\/em> to include the math library.<\/p>\n\/usr\/lib<\/code> folder in Unix, though the location can vary depending on the compiler. The math library goes by various names, but its abbreviation is m<\/code> (lowercase M). To direct the linker to include the library, you must specify a linker switch when you compile:<\/p>\nclang -lm 0618.c<\/code><\/pre>\n