how to print only N numbers of string

Hello all
beginners question :
i have code that receives string buffer the buffer size is 128
but i like to print to console the string that actually receives , it can be 10 characters long or 5 or 20
i have :

Code:

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int rec_result;

int lens = 128;

char buf[128];

rec_result = recv(new_fd,(char*)buf,lens,0);

// now i like to print only the buf string
// this code dos not work because i can't set the char array like this
// what is the alternative ?

int u = rec_result+1;

char bufprintout[6];

strncpy(bufprintout,buf,rec_result);

bufprintout[rec_result+1]='\0';

printf("server recv:%s",bufprintout);

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what is the proper way to do that ?

You could make buf to contain one extra char, and then just set a '\0' at location buf[rec_result] (provided rec_result is not signifying an error).