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首页 > 解决方案 > 如何检测未终止的注释并向我的代码中的标准错误流写入一条错误消息“错误：第 X 行：未终止的注释”？

c - 如何检测未终止的注释并向我的代码中的标准错误流写入一条错误消息“错误：第 X 行：未终止的注释”？

问题描述

#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;
}

这是一个简单的取消注释 C 程序（这是 C 预处理器作业）。/* example当检测到标准错误流的未终止注释 () 时，我正在努力添加一个写入错误消息的功能。错误应该说类似于Error: line X: unterminated commentX 是发生错误的行号。我已经尝试了好几天了，但我无法取得任何进展，我非常沮丧。所以请有人帮助我简单而中肯的答案。

test.txt 

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

程序运行后 test.txt 的结果应该是这样的

hello
world
me
again

它们都在单独的行中，因为 \n 在每种情况下都存在。但我现在得到的是

hello\nworld
Me again

标签： c

解决方案

如果在扫描m_cmnt()时遇到错误消息，您可以修改该函数以输出错误消息：EOF*/

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，则必须随时跟踪行数。

另请注意，您也应该处理//注释并更准确地解析字符串，处理转义序列。

这是一个带有行号处理的版本：

#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;
}

为了说明，这是一个更完整的程序，它处理字符和字符串常量以及转义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;
}

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