compiler-warnings

问题 Consider the following code in strange.cpp : #include <vector> using namespace std; int i = 0; int *bar() { ++i; return &i; } int main() { for(size_t j = 0; j < 99999999999; ++j) // (*) { const auto p = bar(); if(!p) // (**) return -1; } } Compiling this with g++ gives a warning: $ g++ --std=c++11 -O3 strange.cpp strange.cpp: In function ‘int main()’: strange.cpp:12:12: warning: iteration 4294967296ul invokes undefined behavior [-Waggressive-loop-optimizations] ++i; ^ strange.cpp:19:9: note:

问题 With -Wsequence-point enabled, GCC should warn user when undefined behavior code is spotted. For example b = a + ++a; should be noticed by GCC and should be reported as "undefined behavior" code (because ISO C doesn't specify the order of evaluating operands for addition). However, I played with the syntax and I tried this one: int *a = malloc(sizeof(int) * 2); a[0] = 1; printf("%d\n", *(a + (*a)++ - *a)); Of course, I got the warning warning: operation on '*a' may be undefined [-Wsequence

问题 I am using Visual Studio 2005 (VS.8.0) and I am looking to enforce the requirement that all class members, not just the public ones, be documented. While trivial to setup Visual Studio to generate warnings when public, protected, or internal protected members are not documented, I am looking for a way to have the private and internal members throw this same warning. Any suggestions? NOTE: I am using warning level 4, am treating Warnings as Errors, and have the Generate XML flag set. 回答1:

问题 Is there a way to configure the VS2008 C# compiler to give a warning for code like this: Int64 x = 123456789000; Int32 y = (Int32)x; 回答1: The whole point of an explicit cast is to say that "I take responsibility for the problem, please just do it." In your trivial case, it would perhaps be easy for the compiler to figure out that the value would not fit in a Int32, and thus produce your warning. However, what about this: Int64 x = CallSomeMethod(); Int32 y = (Int32)x; How can it warn you

问题 Have a look at this Scala class: class Example { val (x, y): (Int, Int) = (1, 2) } Compiling this results in a warning: Example.scala:2: warning: non variable type-argument Int in type pattern (Int, Int) is unchecked since it is eliminated by erasure val (x, y): (Int, Int) = (1, 2) ^ Removing the explicit type annotation gets rid of this warning: class Example { val (x, y) = (1, 2) } Why do I get the warning and why does removing the explicit type annotation get rid of it? As far as I can see

问题 For code, while(1) { /* ..... */ } MSVC generates the following warning. warning C4127: conditional expression is constant MSDN page for the warning suggests to use for(;;) instead of while(1) . I am wondering what advantage for(;;) is giving and why it warns for the constant usage in while ? What flag should I use on GCC to get the same warning? 回答1: Constant conditionals are often enough simply bugs. Consider this: unsigned k; ... while (k>=0) { ... } The condition k>=0 would make sense if

问题 I'm trying compile program using function gethostbyname() with the cross compiler arm-none-linux-gnueabi , but it did not work when I run my binary on android. My code in below: /* gethostbyname-example.c */ #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <netdb.h> extern int h_errno; int main(int argc,char **argv) { int x, x2; struct hostent *hp; for ( x=1; x<argc

问题 When I executed the code of this question, I got this warning: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long int' [-Wformat=] printf("P-Q: %d, P: %d, Q: %d", (p - q), p, q); ~^ ~~~~~~~ %ld As a reflex fix, I used %ld to print the subtraction of two pointers. And the compiler agreed. Fortunately, I saw a comment from another user mentioning that %td should be used, since the result type of the subtraction is ptrdiff_t . This answer confirms this claim. Now

问题 Typing man strptime it sais that this function needs to have declared _XOPEN_SOURCE and included time.h header. I did it. But, when I try to compile my code I get: ./check.c:56: warning: implicit declaration of function ‘strptime’ Look at my code: int lockExpired(const char *date, const char *format, time_t current) { struct tm *tmp = malloc(sizeof(struct tm *)); time_t lt; int et; strptime(date, format, tmp); lt = mktime(tmp); et = difftime(current, lt); if (et < 3600) return -et; return 1;

问题 I would like to have my warnings set to the highest level using Microsoft Visual C++ compiler. Similar to using -pedantic on gcc. What compiler switches do you use to have the most warnings enabled? 回答1: The highest warning level on Visual C++ is /Wall. The warning level can also be set numerically with /W0, /W1, ... /W4 to generate increasing levels of warnings. The compiler will also check for 64 bit portability issues with /Wp64. And you can tell it to treat warnings as errors with /WX