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gcc较高版本的一些编译警告收集

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!

1、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

2、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。

3、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;

5、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();

6、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

7、

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

本文固定链接: http://www.latelee.org/programming-under-linux/gcc-warning.html

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