Question

#include <stdio.h>
#include <stdbool.h>

void m_cmnt(FILE *fp) {
    int prev;
    int ch;
    while ((ch = getc(fp)) != EOF) {
        if (prev == '*' && ch == '/') {
            return;
        } else
            prev = ch;
    }
}

int main(int c, char **arr) {
    FILE *fp, *np;
    int ch, prev;
    bool String = 0;

    fp = fopen("test.txt", "r");
    np = fopen("temp.txt", "w");

    if (fp == NULL) {
        printf("Invalid/No Filename given as Argument ! \n");
        return 1;
    }
    while ((ch = getc(fp)) != EOF) {
        if (!String) {
            if (ch == '/') {
                prev = ch;
                ch = getc(fp);
                switch (ch) {
                case '*':
                    /* if(ch != 'a') putc('h', np); */
                    m_cmnt(fp);
                    putc(' ', np);
                    break;
                default:
                    putc(prev, np);
                    putc(ch, np);
                    break;
                }
            } else
                putc(ch, np);
        } else
            putc(ch, np);

        if (ch == '\"' || ch == '\'')
            String = !String;
        prev = ch;
    }

    fclose(fp);
    fclose(np);
    remove(arr[1]);
    //rename("temp.txt", arr[1]);
    return 0;
}

这是一个简单的注释掉的C程序（它是C预处理程序的工作）。当检测到标准错误流中的未终止注释（/* example）时，我在添加一项功能以编写一条错误消息时很费劲。错误应该说类似Error: line X: unterminated comment，其中X是发生错误的行号。我已经尝试了好几天了，但是我没有任何进展，我感到非常沮丧。因此，请有人帮助我提供简单明了的答案。

test.txt 

hello\nworld
Me/*some\ncomment*/again

程序运行后的test.txt结果应该是

hello
world
me
again

它们两个都位于单独的行中，因为在每种情况下都存在\ n。但是我现在得到的是

hello\nworld
Me again

Answer 1

如果在扫描m_cmnt()时遇到EOF，您可以修改*/函数以输出错误消息：

void m_cmnt(FILE *fp) {
    int prev, ch;
    for (prev = 0; (ch = getc(fp)) != EOF; prev = ch) {
        if (prev == '*' && ch == '/')
            return;
    }
    fprintf(stderr, "error: unterminated comment\n");
}

如果要输出行号，则必须随时随地跟踪行数。

请注意，您也应该处理//条注释，并更准确地解析字符串，以处理转义序列。

以下是具有行号处理的版本：

#include <stdio.h>
#include <stdbool.h>

/* skip a C multi-line comment, return the last byte read or EOF */
int m_cmnt(FILE *fp, int *lineno_p) {
    int prev, ch, replacement = ' ';
    for (prev = 0; (ch = getc(fp)) != EOF; prev = ch) {
        if (ch == '\n') {
            replacement = '\n';
            ++*lineno_p;
        }
        if (prev == '*' && ch == '/')
            return replacement;
    }
    return EOF;
}

int main(int c, char **arr) {
    FILE *fp, *np;
    int ch;
    bool String = 0;
    const char *filename = "test.txt";
    int lineno = 1;

    fp = fopen(filename, "r");
    np = fopen("temp.txt", "w");

    if (fp == NULL) {
        printf("cannot open input file %s\n", filename);
        return 1;
    }
    while ((ch = getc(fp)) != EOF) {
        if (ch == '\n')
            lineno++;
        if (!String) {
            if (ch == '/') {
                ch = getc(fp);
                if (ch == '\n')
                    lineno++;
                if (ch == '*') {
                    int startline = lineno;
                    ch = m_cmnt(fp, &lineno);
                    if (ch == EOF) {
                        fprintf(stderr, "%s:%d: error: unterminated comment started on line %d\n",
                                filename, *lineno, startline);
                        break;
                    }
                    putc(ch, np);
                } else {
                    putc('/', np);
                    putc(ch, np);
                }
            } else {
                putc(ch, np);
            }
        } else {
            putc(ch, np);
        }

        if (ch == '\"' || ch == '\'')
            String = !String;
    }

    fclose(fp);
    fclose(np);
    remove(arr[1]);
    //rename("temp.txt", arr[1]);
    return 0;
}

为说明起见，这是一个更完整的程序，可以处理字符和字符串常量以及转义的换行符的所有特殊情况：

/* strip C comments by chqrlie */

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

/* read the next byte from the C source file, handing escaped newlines */
int getcpp(FILE *fp, int *lineno_p) {
    int ch;
    while ((ch = getc(fp)) == '\\') {
        if ((ch = getc(fp)) != '\n') {
            ungetc(ch, fp);
            return '\\';
        }
        ++*lineno_p;
    }
    if (ch == '\n')
        ++*lineno_p;
    return ch;
}

int main(int argc, char *argv[]) {
    FILE *fp = stdin, *ft = stdout;
    const char *filename = "<stdin>";
    int ch, lineno;

    if (argc > 1) {
        if ((fp = fopen(filename = argv[1], "r")) == NULL) {
            fprintf(stderr, "Cannot open input file %s: %s\n",
                    filename, strerror(errno));
            return 1;
        }
    }
    if (argc > 2) {
        if ((ft = fopen(argv[2], "w")) == NULL) {
            fprintf(stderr, "Cannot open output file %s: %s\n",
                    argv[2], strerror(errno));
            return 1;
        }
    }
    lineno = 1;
    while ((ch = getcpp(fp, &lineno)) != EOF) {
        int startline = lineno;
        if (ch == '/') {
            if ((ch = getcpp(fp, &lineno)) == '/') {
                /* single-line comment */
                while ((ch = getcpp(fp, &lineno)) != EOF && ch != '\n')
                    continue;
                if (ch == EOF) {
                    fprintf(stderr, "%s:%d: unterminated single line comment\n",
                            filename, startline);
                    break;
                }
                putc('\n', ft);  /* replace comment with newline */
                continue;
            }
            if (ch == '*') {
                /* multi-line comment */
                int lastc = 0, replacement = ' ';
                while ((ch = getcpp(fp, &lineno)) != EOF) {
                    if (ch == '/' && lastc == '*') {
                        break;
                    }
                    if (ch == '\n')
                        replacement = '\n';
                    lastc = ch;
                }
                if (ch == EOF) {
                    fprintf(stderr, "%s:%d: unterminated comment\n",
                            filename, startline);
                    break;
                }
                putc(replacement, ft);  /* replace comment with single space */
                continue;
            }
            putc('/', ft);
            /* keep parsing to handle n/"a//"[i] */
        }
        if (ch == '\'' || ch == '"') {
            int sep = ch;
            const char *const_type = (ch == '"') ? "string" : "character";

            putc(sep, ft);
            while ((ch = getcpp(fp, &lineno)) != EOF) {
                putc(ch, ft);
                if (ch == sep)
                    break;;
                if (ch == '\\') {
                    if ((ch = getcpp(fp, &lineno)) == EOF)
                        break;
                    putc(ch, ft);
                }
                if (ch == '\n') {
                    fprintf(stderr, "%s:%d: unescaped newline in %s constant\n",
                            filename, lineno - 1, const_type);
                    /* This is a syntax error but keep going as if constant was terminated */
                    break;
                }
            }
            if (ch == EOF) {
                fprintf(stderr, "%s:%d: unterminated %s constant\n",
                        filename, startline, const_type);
                break;
            }
            continue;
        }
        putc(ch, ft);
    }
    if (fp != stdin)
        fclose(fp);
    if (ft != stdout)
        fclose(ft);
    return 0;
}

我该如何检测未终止的注释，并在代码中的标准错误流中写一条错误消息“错误：X行：未终止的注释”？

1 个答案: