Socket programming in C/C++ - gcc char * warning

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Deprecated conversion from string constant to char * error

I'm writting a program in C/C++ which is attempting to communicate over a UDP socket.

The code I'm working on has a variable, char *servIP, which is set through an input parameter to the main function. However, I want the input parameter to be optional, so I have the code:

if(argc > 1)
    servIP = argv[1];           /* First arg: server IP address (dotted quad) */
else
    servIP = "127.0.0.1";

servIP later gets converted into a more network-usable form.

When I compile this, I get a warning saying "warning: deprecated conversion from string constant to char*".

I assume this isn't the correct way to enter that IP address; what is a better way?

http://stackoverflow.com/questions/8126512/deprecated-conversion-from-string-constant-to-char has your answer — mfsiega, Oct 14 '12 at 01:26
Just a note that you could eventually check if the content of `argv[1]` is a valid IP address. — ForceMagic, Oct 14 '12 at 01:55
do you realise, that your question has nothing to do with "Socket programming", "UDP".. ? — Karoly Horvath, Oct 14 '12 at 03:08
Are you programming in C or in C++? They're two different languages. — Keith Thompson, Oct 14 '12 at 03:26
problem solution, found thanks to @Karoly Horvath, is just to do: char ip[] = "127.0.0.1"; servIP = ip; — Gossamer Shadow, Oct 14 '12 at 06:18

jspcal · Answer 1 · 2012-10-14T01:37:43.780

declare servIP as a const char * instead of char * or, if that's not possible, strdup("127.0.0.1") (in the second case, just remember to free it later)

the effect of modifying a string literal is undefined, which is why c++ assigns the type "array of n const char" to a string literal. the compiler is warning you about the conversion from a const data type to a non-const one.

you can use std::string instead, and then when you need a C-style pointer to the underlying characters, you can use std::string::c_str().

Socket programming in C/C++ - gcc char * warning

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