passing argument 1 of 'strlen' differ in signedness

c strlen
sakthi picture sakthi · Nov 27, 2014 · Viewed 15.2k times · Source

I use strlen() call all over my project, until now I compiled my project without -Wall compiler option. But when I start using -Wall I face so many compiler warning. 80% are the strlen char * vs const char * warning.

I am aware of type casting all strlen() calls. Is there any other way that I can suppress the following warning?

./Proj.c:3126: warning: pointer targets in passing argument 1 of 
    'strlen' differ in signedness`

C:/staging/usr/include/string.h:397: note: expected 'const char *' but 
    argument is of type 'unsigned char *'`

Answer

Bathsheba picture Bathsheba · Nov 27, 2014

strlen takes a const char* as its input.

Unfortunately the C standard states that signedness of char is down to the compiler and platform. Many programmers therefore opt to set the signedness of char explicitly using signed char or unsigned char.

But doing that will cause warnings to be emitted if char* has the other sign convention to what you expect.

Luckily in the context of strlen, taking a C-style cast is safe: use strlen((const char*)...);

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