断开字符串指针直到c中的标记

Question

I have a pointer char * c = "I - need - to - do - this - break". I need to break it according to the '-' such that in each iteration I get an output as "I" then "I -need" then " I - need - to" and so on till the whole string. Any help?

Answer 1

The simple way is to make c mutable and not a pointer to a String Literal . That way all you need to do is work down the string (either using a pointer or an index) and keep track of whether you are in a word or not in a word. When you hit a space (or hyphen if you get rid of the spaces), if you are in a word, save the current char, overwrite the current char in the array with '\\0' to terminate the string at the current character and print it. Restore the current character in the array and repeat until you run out of characters, eg

#include <stdio.h>

int main (void) {

    char c[] = "I - need - to - do - this - break", /* an array */
        *p = c;     /* pointer to current char */
    int in = 0;     /* flag for in/out of word */

    while (*p) {    /* loop over each char */
        if (*p == ' ' || *p == '-') {   /* if a space or hyphen */
            if (in) {                   /* if in a word */
                char current = *p;      /* save current char */
                *p = 0;                 /* nul-terminate array at current */
                puts (c);               /* print array */
                *p = current;           /* restore current in array */
                in = 0;                 /* set flag out of word */
            }
        }
        else {          /* otherwise, not a space or hyphen */
            in = 1;     /* set flag in word */
        }
        p++;            /* advance to next char */
    }

    if (in)             /* if in word when last char reached */
        puts (c);       /* output full string */
}

Example Use/Output

$ ./bin/incremental
I
I - need
I - need - to
I - need - to - do
I - need - to - do - this
I - need - to - do - this - break

Using a Non-Mutable String Literal

If you must use a non-mutable String Literal , then the approach is largely the same. The only difference being you cannot nul-terminate the original string, so you are left using another pointer (or index) to output each character from the beginning until you reach the current using putchar (or getting the number of characters from p - c and then copying to a buffer to nul-terminate and output all at once). Simply looping until you reach the current and using putchar for output is about as easy as anything else, eg

#include <stdio.h>

int main (void) {

    char *c = "I - need - to - do - this - break",  /* string literal */
        *p = c;     /* pointer to current char */
    int in = 0;     /* flag for in/out of word */

    while (*p) {    /* loop over each char */
        if (*p == ' ' || *p == '-') {   /* if a space or hypen */
            if (in) {                   /* if in a word */
                char *wp = c;           /* get pointer to start */
                while (wp < p)          /* loop until you reach current */
                    putchar (*wp++);    /* output each char & increment */
                putchar ('\n');         /* tidy up with newline */
                in = 0;                 /* set flag out of word */
            }
        }
        else {          /* otherwise, not a space or hyphen */
            in = 1;     /* set flag in word */
        }
        p++;            /* advance to next char */
    }

    if (in)             /* if in word when last char reached */
        puts (c);       /* output full string */
}

(the output is the same)

Look things over and let me know if you have questions.