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最近整理了下代码警告问题。这里记录一下。关于此问题应该具体问题具体分析,有的警告是不伤大雅,对于编码规范严格的团队,则需要消除;而有的警告则可能有隐患,需要解决。
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