math.h

问题 This question already has an answer here: Why am I getting “undefined reference to sqrt” error even though I include math.h header? [duplicate] 5 answers I don't know if I'm missing something obvious, but it appears that I'm unable to compute square roots of a variable in C; the sqrt() function only seems to work on constants. This is my code: #include <math.h> #include <stdio.h> int main() { double a = 2.0; double b = sqrt(a); printf("%f", b); return 0; } When I run this program, I get the

问题 For the following C source code: #include <math.h> int main(void) { double x; x = log(0.0); return 0; } When I compile with gcc -lm , I got: /tmp/ccxxANVH.o: In function `main': a.c:(.text+0xd): undefined reference to `log' collect2: error: ld returned 1 exit status But, if I replace log(0.0) with log(10.0) , then it can compile successfully. I don't quite understand this, since no matter they make mathematical sense or not, they should compile -- there is no syntax error. Could anyone

问题 If I include <stdlib.h> or <stdio.h> in a C program I don\'t have to link these when compiling but I do have to link to <math.h> , using -lm with gcc, for example: gcc test.c -o test -lm What is the reason for this? Why do I have to explicitly link the math library but not the other libraries? 回答1: The functions in stdlib.h and stdio.h have implementations in libc.so (or libc.a for static linking), which is linked into your executable by default (as if -lc were specified). GCC can be

问题 What is the difference between atan and atan2 in C++? 回答1: std::atan2 allows calculating the arctangent of all four quadrants. std::atan only allows calculating from quadrants 1 and 4. 回答2: From school mathematics we know that the tangent has the definition tan(α) = sin(α) / cos(α) and we differentiate between four quadrants based on the angle that we supply to the functions. The sign of the sin , cos and tan have the following relationship (where we neglect the exact multiples of π/2 ):

问题 #include <stdio.h> #include <stdlib.h> #include <math.h> int main() { int n,i,ele; n=5; ele=pow(n,2); printf(\"%d\",ele); return 0; } The output is 24 . I\'m using GNU/GCC in Code::Blocks. What is happening? I know the pow function returns a double , but 25 fits an int type so why does this code print a 24 instead of a 25 ? If n=4; n=6; n=3; n=2; the code works, but with the five it doesn\'t. 回答1: Here is what may be happening here. You should be able to confirm this by looking at your

问题 If I include <stdlib.h> or <stdio.h> in a C program I don\'t have to link these when compiling but I do have to link to <math.h> , using -lm with gcc, for example: gcc test.c -o test -lm What is the reason for this? Why do I have to explicitly link the math library but not the other libraries? 回答1: The functions in stdlib.h and stdio.h have implementations in libc.so (or libc.a for static linking), which is linked into your executable by default (as if -lc were specified). GCC can be