最近整理了下代码警告问题。这里记录一下。
在以前某个项目上竟然用-w把gcc的警告给关闭了，怪不得编译代码完全没警告，多漂亮的代码！

未使用变量、未使用函数返回值， 未使用变量：

warning: unused variable ‘ret’ [-Wunused-variable]
  int ret;

–>修改：删之。

没有达到函数末尾：

warning: control reaches end of non-void function [-Wreturn-type]
int open(const char* file)
{
     if(foo==11)
     {
          return ok;
     }
     // -->修改：此处要加上返回值
}

没有返回值：

warning: no return statement in function returning non-void [-Wreturn-type]
  int Open(char* file){}

–> 修改：加上返回值

参数一致性，参数类型检查

空字符串：

warning: zero-length gnu_printf format string [-Wformat-zero-length]
         sprintf(buffer, "");

类型不对：

warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘char*’ [-Wformat=]
warning: format ‘%d’ expects argument of type ‘int*’, but argument 4 has type ‘short int*’ [-Wformat=]

–> 修改：按printf格式来修改，unsigned long使用%lu。不要用%d来打印字符串指针。
有符号和无符号：

warning: pointer targets in passing argument 2 of ‘ll_foobar’ differ in signedness [-Wpointer-sign]
expected ‘unsigned char *’ but argument is of type ‘char *’

有符号和无符号比较：

warning: comparison between signed and unsigned integer expressions [-Wsign-compare]

–> 修改：强制转换类型
参数类型：

warning: passing NULL to non-pointer argument 2 of ‘void* memset(void*, int, size_t)’ [-Wconversion-null]
  memset(foobar, NULL, sizeof(foobar));
(C++中，NULL是指针，不是数值，而memset要求的是数值0)

–> 修改：用0来代替，或将NULL强转为INT。
比较诡异：

warning: argument to ‘sizeof’ in ‘char* strncpy(char*, const char*, size_t)’ call is the same expression as the destination; did you mean to provide an explicit length? [-Wsizeof-pointer-memaccess]
   strncpy(ptr, buffer, sizeof(ptr));

用意本身是好的，用法却是错的，ptr是指针，sizeof指针只能得到4。
类似的有：

warning: argument to ‘sizeof’ in ‘void* memset(void*, int, size_t)’ call is the same expression as the destination; did you mean to dereference it? [-Wsizeof-pointer-memaccess]
   memset(this, 0, sizeof(this));

–> 修改：strncpy、memset第三个参数按实际给数值。
C++类构造函数初始化顺序问题：

warning: CFoobar::m_nInit will be initialized after [-Wreorder]
  int m_nInit;
       ^
warning:   ‘int CFoobar::m_nTime’ [-Wreorder]
  int m_nTime’;

–> 修改：按声明的顺序排列。
常量字符串：

warning: deprecated conversion from string constant to ‘CHAR* {aka char*}’ [-Wwrite-strings]

–> 修改：字符串要加const。

打印格式化

warning: too few arguments for format
warning: too many arguments for format

如本身要打印2个参数，但只有一个%。myprintf("hello world %d!\n", count, getname());
–>修改：认真检查参数。

4、类型一致性，类型转换

整数溢出：

warning: integer overflow in expression [-Woverflow]
#define BIG_SIZE 800*1024*1024*1024

转换转换：

warning: narrowing conversion of ‘height’ from ‘DWORD {aka unsigned int}’ to ‘int’ inside { } is ill-formed in C++11 [-Wnarrowing]
     my_dst_size foo = {width, height};

my_dst_size类型为int，但width和height为DWORD
–>修改：强制转换类型，保持一致。

warning: extended initializer lists only available with -std=c++11 or -std=gnu++11 [enabled by default]
     my_pos.pos = {0,0};

my_pos.pos为坐标。
–>修改：一一赋值。

my_pos.pos.x = 0;
my_pos.pos.y = 0;

括号、优先级

warning: suggest parentheses around arithmetic in operand of '^' [-Wparentheses]
#define HELLO  ((((z>>51)^(y<<32))+((y>>23)^(z<<5)))^((sum^y)+(k[p&7^e]^z)))

–> 添加括号

#define HELLO  ((((z>>51)^(y<<32))+((y>>23)^(z<<5)))^((sum^y)+(k[(p&7)^e]^z)))

另一个例子：

warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
       return id == foo::Get() || foo::Get() != bar::Get() && bar::Go();

switch

warning: enumeration value ‘LL_FOO’ not handled in switch [-Wswitch]

–>枚举类型没有完全使用，如没有default语句。添加之

地址总为真

warning: the address of ‘filename’ will always evaluate as ‘true’ [-Waddress]
#define LL_STR(foo)    foo ? foo : ""

其它

error: function declaration isn’t a prototype

–>函数声明如无参数，要加上void

李迟 2015.4.22周三中午