printf - Weird Symbols printed at end of string - C -

so, i've got program parses expressions in line of text such as

11110000 & 11001100 ; 

and evaluates binary results. code parsing correctly , evaluating correctly, 2 of test inputs (including 1 above) printf printing these weird symbols after each run.

eos$ ./interpreter < program02.txt 11000000 + eos$ ./interpreter < program02.txt 11000000 2ñ eos$ ./interpreter < program02.txt 11000000 "] eos$ ./interpreter < program02.txt 11000000 ÒØ eos$ ./interpreter < program02.txt 11000000 Ê eos$ ./interpreter < program02.txt 11000000 òj 

the string malloc'd this

char *str = ( char * ) malloc ( ( getlength( src ) + 1 ) * sizeof( char ) ); 

and here how string printed

char *str = binarytostring( val ); printf( "%s\n", str ); 

any awesome! thanks!

strings null terminated in c. when malloc() memory, filled whatever in block previously.

one solution fill buffer null character \0 via memset() (found in string.h) after using malloc() so:

int strlen = getlength(src) + 1; char *str = (char*)malloc(strlen * sizeof(char)); memset(str, '\0', strlen); // fill null chars 

equally write \0 after final character.

edit: not advice according iharob's comment. taking account, , given know length of string:

int strlen = getlength(src) + 1; char *str = calloc(strlen, sizeof(char)); // allocate strlen * sizeof(char) if (str == null) {     // error allocating str - handle error } str[strlen - 1] = '\0'; // zero-based, char after final character 

is better solution.