CODEWITHSUNDEEP
cstringmallocnull-terminated
Tom Dara
Tom Dara

Reputation: 61

c malloc() - do I need to allocate space for the null terminator

I have a snippet of code below that appends the text _dut1_serial_log.txt to a supplied filename. The supplied filename is a variable in the struct pointed to by targetP.

The text _dut1_serial_log.txt is 20 chars long. My question is do I need the +1 when I call malloc for the null terminator? 

char *filename_ending = "_dut1_serial_log.txt";
    char *filename_with_extension;
    prv_instance_t *targetP = threadParams->targetP;

    /*append filename ending "_dut1_serial_log.txt" to filename supplied*/
    filename_with_extension = malloc(strlen(targetP->output_filename)+1+20);
    strcpy(filename_with_extension, targetP->output_filename); /* copy name into the new var */
    strcat(filename_with_extension, filename_ending); /* add the extension */

Upvotes: 2

Views: 1784

Answers (1)

Bathsheba
Bathsheba

Reputation: 234715

Both strcpy and strcat will copy the NUL-terminator from the source string to the destination buffer.

You do need to reserve space for that terminator in the destination buffer therefore.

To avoid any doubt, "_dut1_serial_log.txt" is a const char[21] type.

Upvotes: 2

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