为什么我可以单独打印每个字符而不是整体打印？

Question

This is one part of a server implementation where I'm going through the request line header and giving output accordingly. This might be a basic question. How come I can print out each character separately but not the string as whole?

Has this something to do with mismanagement of memory?

This is part of pset6 in CS50 .

 #include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 int
 main(int argc, char * argv[])
 {
    char* line = "GET /cat.html HTTP/1.1";

    char* method = strstr(line, "GET");
    if (strcmp(method, line) != 0)
    {
        printf("405 Method Not Allowed");
    }

    printf("%s\n", line);

    char* requestTarget = malloc(10);
    char* ch = strchr(line,'/');
    if (ch != NULL)
    {
        int i = 0;
        for (i = (ch-line); i < strlen(line)-9; i++)
        {
            requestTarget[i] = line[i];
            printf("%c", requestTarget[i]);
        }
        requestTarget[i] = '\0';
    }

    else
         printf(" 501 Not Implemented");

    printf("requestTarget: %s\n", requestTarget);

    free(requestTarget);
    return 0;
 } 

A side note, I know it's bad pratice to hard code in -9 in my for lop strlen(line)-9 . But I couldn't figure out how to just read the characters in the requested target cat.html . And I know that the header is specified by method SP request-target SP HTTP-version CRLF (is CRLF aka \\r\\n two characters?) So -9 works (I think) but maybe not the best.

EDIT: I edited my loop so that I add an null terminator at the end. This was originally meant to be in, but since I have edited my code so much now it was mistakenly taken out. It still does not work though.

Answer 1

Your code has undefined behavior, because it writes past the space that you allocated.

You do this copy

requestTarget[i] = line[i];

when i points to some location in the middle of the line[] , but requestTarget requires a smaller index. You need to "translate" the index, or create a separate one for the destination:

int j = 0;
for (int i = (ch-line); i < strlen(line)-9; i++, j++)
{
    requestTarget[j] = line[i];
    printf("%c", requestTarget[j]);
}
requestTarget[j] = '\0';

Note: you need to make sure that requestTarget has enough space for the characters that you wish to store in it, including the null terminator.