Arrays and Strings

String Length

A string scan usually stops when it reaches the null terminator.

scan A scan moves one character at a time through an array.
terminator check Stopping at `'\0'` prevents hidden buffer contents from being treated as text.

String Length

stopAtNull
string_length.c
Replay: real traced execution (multi-file project)
#include <stdio.h>

int main(void) {
    char text[5] = {'h', 'i', '\0', 'x', '\0'};
    int stopAtNull = 1;
    int length = 0;

    while (length < 5) {
        if (stopAtNull && text[length] == '\0') {
            break;
        }
        length++;
    }

    printf("length=%d\n", length);
    return 0;
}

#include <stdio.h>

int main(void) {
    char text[5] = {'h', 'i', '\0', 'x', '\0'};
    int stopAtNull = 0;
    int length = 0;

    while (length < 5) {
        if (stopAtNull && text[length] == '\0') {
            break;
        }
        length++;
    }

    printf("length=%d\n", length);
    return 0;
}

  1. text ← hi, stopAtNull ← 1, length ← 0

    3int main(void) {4    char text→ hi[5] = {'h', 'i', '\0', 'x', '\0'};5    int stopAtNull→ 1 = 1; //@stopAtNull=06    int length→ 0 = 0;

  2. length ← 1

    pass 1 of 3
    8while (length0 < 5) {9    if (stopAtNull && text[length] == '\0') {10        break;11    }12    length→ 1++;13}
    All 3 passes — pass 1 is the card above
    passstopAtNulltext[length]length
    1——0 → 1
    2——1 → 2
    312

  3. if (stopAtNull && text[length] == '\0')

    8while (length < 5) {9    if (stopAtNull1 && text[length] == '\0') {10        break;11    }

  4. printf("length=%d ", length);

    15    printf("length=%d\n", length2);16    return 0;17}
    outputlength=2

  1. text ← hi, stopAtNull ← 0, length ← 0

    3int main(void) {4    char text→ hi[5] = {'h', 'i', '\0', 'x', '\0'};5    int stopAtNull→ 0 = 0;6    int length→ 0 = 0;

  2. length ← 1

    pass 1 of 5
    8while (length0 < 5) {9    if (stopAtNull && text[length] == '\0') {10        break;11    }12    length→ 1++;13}
    All 5 passes — pass 1 is the card above
    passlength
    10 → 1
    21 → 2
    32 → 3
    43 → 4
    54 → 5

  3. printf("length=%d ", length);

    15    printf("length=%d\n", length5);16    return 0;17}
    outputlength=5