一条完整的流水线

（本条路线统一用 gcc -std=c11 -O0 -Wall 编译）写文件 → 读回来 → 存进堆 → 算 → 全部还回去：

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

static int got = 0, gave = 0;      /* l1_lang_05 那块仪表盘接着用 */

int main(void) {
    FILE *f = tmpfile();
    if (f == NULL) { printf("建不出\n"); return 1; }

    const char *rows[4] = {"apple 3", "pear 5", "plum 2", "fig 4"};
    for (int i = 0; i < 4; i++) fprintf(f, "%s\n", rows[i]);
    rewind(f);

    /* 边读边把每行存进堆上的一份副本 */
    char **kept = malloc(4 * sizeof(char *));
    got++;
    int n = 0;
    char name[32];
    int qty, total = 0;
    while (n < 4 && fscanf(f, "%31s %d", name, &qty) == 2) {
        kept[n] = malloc(strlen(name) + 1);
        got++;
        strcpy(kept[n], name);
        total += qty;
        n++;
    }
    fclose(f);

    int longest = 0;
    for (int i = 0; i < n; i++)
        if ((int)strlen(kept[i]) > longest) longest = (int)strlen(kept[i]);

    for (int i = 0; i < n; i++) { free(kept[i]); gave++; }
    free(kept); gave++;

    printf("%d/%d/%d/%d\n", n, total, longest, got - gave);
    return 0;
}