您可以编写一个能够处理大多数情况的状态机。
当您扫描文件时，您将处于以下状态之一：
- TEXT - 常规（非注释）文本；这是您将要开始的状态。在此状态下看到的任何换行都会导致总行数计数器增加。
- SAW_SLASH - 您已经看到了一个
/，它可能是单行或多行注释的开头。如果下一个字符是/，您将进入 SINGLE_COMMENT 状态。如果下一个字符是*，您将进入 MULTI_COMMENT 状态。对于任何其他字符，您将返回 TEXT 状态。
- SINGLE_COMMENT - 您已经看到了
// 令牌；你会一直保持这个状态，直到你看到一个换行符；一旦看到换行符，您将增加单行 cmets 的数量以及总行数，然后返回 TEXT 状态。
- MULTI_COMMENT - 你已经看到了
/* 令牌；在看到下一个 */ 令牌之前，您将保持此状态。您在此状态下看到的任何换行符都会导致多注释行计数器与总行数一起增加。
- SAW_STAR - 在 MULTI_COMMENT 状态下，您看到了一个
*。如果下一个字符是/，您将返回 TEXT 状态。如果下一个字符是*，您将停留在 SAW_STAR 状态。否则，您将返回 MULTI_COMMENT 状态。
有一些我没有处理的极端情况（例如在评论状态下遇到 EOF），但以下应该是一个合理的示例，说明如何执行此类操作。
请注意，嵌套的 cmets 不会被计算在内；即，如果 //-delimited 评论出现在 /* */-delimited 评论中，则只会更新多评论计数器。
您可能希望将计数逻辑分解到它自己的函数中；只是尽量让这个例子简单明了。
#include <stdio.h>
#include <stdlib.h>
/**
* Count up the number of total lines, single-comment lines,
* and multi-comment lines in a file.
*/
int main(int argc, char **argv)
{
FILE *fp;
int c;
unsigned int chars = 0;
unsigned int total = 0;
unsigned int multi = 0;
unsigned int single = 0;
enum states { TEXT,
SAW_SLASH,
SAW_STAR,
SINGLE_COMMENT,
MULTI_COMMENT } state = TEXT;
if ( argc < 2 )
{
fprintf(stderr, "USAGE: %s <filename>\n", argv[0]);
exit(0);
}
fp = fopen( argv[1], "r" );
if ( !fp )
{
fprintf(stderr, "Cannot open file %s\n", argv[1] );
exit(0);
}
while ( (c = fgetc( fp )) != EOF )
{
chars++;
switch( state )
{
case TEXT :
switch( c )
{
case '/' : state = SAW_SLASH; break;
case '\n' : total++; // fall-through
default : break;
}
break;
case SAW_SLASH :
switch( c )
{
case '/' : state = SINGLE_COMMENT; break;
case '*' : state = MULTI_COMMENT; break;
case '\n' : total++; // fall through
default : state = TEXT; break;
}
break;
case SAW_STAR :
switch( c )
{
case '/' : state = TEXT; multi++; break;
case '*' : break;
case '\n' : total++; multi++; // fall through
default : state = MULTI_COMMENT; break;
}
break;
case SINGLE_COMMENT :
switch( c )
{
case '\n' : state = TEXT; total++; single++; // fall through
default : break;
}
break;
case MULTI_COMMENT :
switch( c )
{
case '*' : state = SAW_STAR; break;
case '\n' : total++; multi++; // fall through
default : break;
}
break;
default: // NOT REACHABLE
break;
}
}
fclose(fp);
printf( "File : %s\n", argv[1] );
printf( "Total lines : %8u\n", total );
printf( "Single-comment lines : %8u\n", single );
printf( "Multi-comment lines : %8u\n", multi );
return 0;
}
编辑
这是一个与上述程序等效的表驱动程序。我创建了一个state 表来控制状态转换和一个action 表来控制当我改变状态时会发生什么。
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
/**
* Using preprocessor macros instead of enums, per request; normally
* I would use enums, since they obey scoping rules and
* show up in debuggers.
*/
#define TEXT 0
#define SAW_SLASH 1
#define SAW_STAR 2
#define SINGLE_COMMENT 3
#define MULTI_COMMENT 4
#define TOTAL_STATES 5
#define NO_ACTION 0
#define INC_TOTAL 1
#define INC_SINGLE 2
#define INC_MULTI 4
/**
* This example assumes 7-bit ASCII, for a total of
* 128 character encodings. You'll want to change this
* to handle other encodings.
*/
#define ENCODINGS 128
/**
* Need a state table to control state transitions and an action
* table to specify what happens on a transition. Each table
* is indexed by the state and the next input character.
*/
static int state[TOTAL_STATES][ENCODINGS]; // Since these tables are declared at file scope, they will be initialized to
static int action[TOTAL_STATES][ENCODINGS]; // all elements 0, which correspond to the "default" states defined above.
/**
* Initialize our state table.
*/
void initState( int (*state)[ENCODINGS] )
{
/**
* If we're in the TEXT state and see a '/' character, move to the SAW_SLASH
* state, otherwise stay in the TEXT state
*/
state[TEXT]['/'] = SAW_SLASH;
/**
* If we're in the SAW_SLASH state, we can go one of three ways depending
* on the next character.
*/
state[SAW_SLASH]['/'] = SINGLE_COMMENT;
state[SAW_SLASH]['*'] = MULTI_COMMENT;
state[SAW_SLASH]['\n'] = TEXT;
/**
* For all but a few specific characters, if we're in any one of
* the SAW_STAR, SINGLE_COMMENT, or MULTI_COMMENT states,
* we stay in that state.
*/
for ( size_t i = 0; i < ENCODINGS; i++ )
{
state[SAW_STAR][i] = MULTI_COMMENT;
state[SINGLE_COMMENT][i] = SINGLE_COMMENT;
state[MULTI_COMMENT][i] = MULTI_COMMENT;
}
/**
* Exceptions to the loop above.
*/
state[SAW_STAR]['/'] = TEXT;
state[SAW_STAR]['*'] = SAW_STAR;
state[SINGLE_COMMENT]['\n'] = TEXT;
state[MULTI_COMMENT]['*'] = SAW_STAR;
}
/**
* Initialize our action table
*/
void initAction( int (*action)[ENCODINGS] )
{
action[TEXT]['\n'] = INC_TOTAL;
action[SAW_STAR]['/'] = INC_MULTI;
action[MULTI_COMMENT]['\n'] = INC_MULTI | INC_TOTAL; // Multiple actions are bitwise-OR'd
action[SINGLE_COMMENT]['\n'] = INC_SINGLE | INC_TOTAL; // together
action[SAW_SLASH]['\n'] = INC_TOTAL;
}
/**
* Scan the input file for comments
*/
void countComments( FILE *stream, size_t *totalLines, size_t *single, size_t *multi )
{
*totalLines = *single = *multi = 0;
int c;
int curState = TEXT, curAction = NO_ACTION;
while ( ( c = fgetc( stream ) ) != EOF )
{
curAction = action[curState][c]; // Read the action before we overwrite the state
curState = state[curState][c]; // Get the new state (which may be the same as the old state)
if ( curAction & INC_TOTAL ) // Execute the action.
(*totalLines)++;
if ( curAction & INC_SINGLE )
(*single)++;
if ( curAction & INC_MULTI )
(*multi)++;
}
}
/**
* Main function.
*/
int main( int argc, char **argv )
{
/**
* Input sanity check
*/
if ( argc < 2 )
{
fprintf( stderr, "USAGE: %s <filename>\n", argv[0] );
exit( EXIT_FAILURE );
}
/**
* Open the input file
*/
FILE *fp = fopen( argv[1], "r" );
if ( !fp )
{
fprintf( stderr, "Cannot open file %s\n", argv[1] );
exit( EXIT_FAILURE );
}
/**
* If input file was successfully opened, initialize our
* state and action tables.
*/
initState( state );
initAction( action );
size_t totalLines, single, multi;
/**
* Do the thing.
*/
countComments( fp, &totalLines, &single, &multi );
fclose( fp );
printf( "File : %s\n", argv[1] );
printf( "Total lines : %zu\n", totalLines );
printf( "Single-comment lines : %zu\n", single );
printf( "Multi-comment lines : %zu\n", multi );
return EXIT_SUCCESS;
}
运行文件本身给我们
$ ./comment_counter comment_counter.c
File : comment_counter.c
Total lines : 150
Single-comment lines : 7
Multi-comment lines : 42
我认为是对的。这与第一个版本具有所有相同的弱点，只是形式不同。