cat

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

void filecopy(FILE *ifp, FILE *ofp) {
    int c;

    while ((c = getc(ifp)) != EOF) { // #define EOF -1
        putc(c, ofp);
    }
}

int main(int argc, char *argv[]) { // 指针数组
    FILE *fp;
    void filecopy(FILE *, FILE *);
    char *prog = argv[0];

    if (argc == 1) { // 只输入函数名字时
        filecopy(stdin, stdout);
    }
    else {
        while (--argc) { // 连续输出多个文件，循环argc－1次
            if ((fp = fopen(*++argv, "r")) == NULL) {
                fprintf(stderr, "%s: can't open %s\n", prog, *argv);
                exit(1);
//                printf("cat: can't open %s\n", *argv);
//                return 1;
            }
            else {
                filecopy(fp, stdout);
                fclose(fp);
            }
        }
    }

    if (ferror(stdout)) {
        fprintf(stderr, "%s: error writing stdout\n", prog);
        exit(2);
    }

    exit(0);
}