我在C中构建一个模式识别器程序，它读入用户定义的字符串和4个字符的用户定义模式。然后程序有一个函数来确定是否找到了一个模式以及最初找到模式（根据输入文本索引）。
我知道这对大多数人来说都是基本的，我只希望能够迅速成为一名更熟练的程序员。当我执行我的程序时，它会以我不理解的方式陷入无限循环。
我知道问题出在我的FindMatch函数上，而不是读入输入文本和模式。我的FindMatch函数有什么问题？！请帮忙。
#include <stdio.h>
#include <stdlib.h>
char *getCharBlock(int *size);
int findmatchA(char *text, char *pattern, int tsize, int psize);
void printIt(char *ptr, int index, int size);
int main(){
char *text, *pattern; //pointers for the characters you will read
char *p,*q,*r; //some pointer variables
int tsize,psize,x,y,z; //some integers
printf("Please input a sequence of character text (characters only will be stored):");
text = getCharBlock(&tsize);
printf(" Now input the pattern you seek to search for: ");
pattern = getCharBlock(&psize);
x = findmatch(text,pattern,tsize, psize);
if(x== -1){
printf("No Match Found \n");
printf("No starting position for match exists \n");
}
else{
printf("Match Has Been Found! \n");
printf("Match starting position at index %d \n", x);
printf("Remaining text after Match: \n");
printIt(text, x+psize, tsize);
}
free(text);
free(pattern);
}
char *getCharBlock(int *size){
char *input = (char*) malloc (80*sizeof(char));
char a;
int i = 0;
a = getchar();
while(i<80 && a!= '\n'){
if( (a>= 'a' && a <= 'z') || (a>= 'A' && a <= 'Z') ){
*(input + i) = a;
i++;
}
a = getchar();
}
*size = i;
return input;
}
int findmatch(char *text, char *pattern, int tsize, int psize) {
int index = 0;
int state = 0;
while (psize <= tsize) {
if ((*(text + index) == *pattern) && state == 0){
state = 1;
index++;
printf( "test 1 \n");
}
else if ((*(text + index) != *pattern) && state == 0){
state = 0;
index++;
printf( "test1.1 \n");
}
else if (*(text + index) == *(pattern + 1) && state ==1) {
state = 2;
index++;
printf( "test 2 \n");
}
else if (*(text + index) != *(pattern + 1) && state ==1) {
state = 0;
printf("test 2.2 \n");
}
else if (*(text + index) == *(pattern + 2) && state ==2) {
state = 3;
printf("test 3 \n");
}
else if (*(text + index) != *(pattern + 2) && state ==2) {
state = 0;
printf("test 3.3 \n");
}
else if (*(text + index) == *(pattern + 3) && state ==3) {
state = 4;
printf("test 4 \n");
}
else if (*(text + index) != *(pattern + 3) && state ==3) {
state = 0;
printf("test 4.4 \n");
}
else {
return -1;
}
index++;
}
return index;
}
答案 0 :(得分：1)
我知道这对你们大多数人来说都是基本的，我希望能够很快 成为一个更熟练的程序员
祝你好运，我给你我的建议。
一些问题阻止程序正常运行。
它以我不喜欢的方式陷入无限循环 理解。
1）你永远在这里循环：
`while (psize <= tsize) {`
psize永远不会改变，永远不会达到tsize，循环永远不会结束。
但这不是唯一的问题。
2）text和pattern的输入字符串未被'\0'.终止注意：
malloc不是calloc。分配的内存可以包含任何内容！
要谨慎，你应该检查，如果记忆分配得当。
3）并非所有州都正确推进index变量：
else if (*(text + index) == *(pattern + 2) && state ==2) {
state = 3; // sg! index++; is missing!
printf("test 3 \n");
}
else if (*(text + index) != *(pattern + 2) && state ==2) {
state = 0;
printf("test 3.3 \n");
}
这可能会妨碍正确的模式匹配。
4）未完成输入验证，例如：您应确保模式的长度恰好为4个字符。
如果我被允许只给你一个建议，那就是："Never, ever use if-else chain!"。将其替换为switch-case-break构造。
您的int findmatch就是一个很好的例子。 if-else链创建丛林难以调试。你的州非常相似，应该创造和谐。
他们不是。您的功能可以用更简单的功能替换：
int findmatch(char *text, char *pattern, int tsize, int psize) {
int index = 0;
int state = 0;
printf("Text=<%s> pattern=<%s> tsize=%d psize=%d \n",text, pattern, tsize, psize);
while (index <= tsize) {
switch (state)
{
case 0:
state = next_state(text,pattern, "test 1", "test1.1", &index, 0, 1, 1);
break;
case 1: // pattern[0] matched
state = next_state(text, pattern, "test 2", "test2.2", &index, 1, 2, 0);
break;
case 2: // pattern [0] [1] matched
state = next_state(text, pattern, "test 3", "test3.3", &index, 2, 3, 0);
break;
case 3: // pattern [0] [1] [2] matched
state = next_state(text, pattern, "test 4", "test4.4", &index, 3, 4, 0);
break;
case 4:
printf("DONE, index = %d \n",index);
return index;
break;
default:
printf("We should not be here! \n");
break;
} // case
} // while
return -1;
}
编程就像创作音乐或绘画一样。你的创作应该很美。有和谐，平衡。
这是您学习的工作计划。
#include <stdio.h>
#include <stdlib.h>
char *getCharBlock(int *size);
int findmatch(char *text, char *pattern, int tsize, int psize);
void printIt(char *ptr, int index, int size);
void printIt(char *ptr, int index, int size)
{
}
int main(void){
char *text, *pattern; // pointers for the characters you will read
int tsize,psize,x; // some integers
printf("Please input a sequence of character text (characters only will be stored):\n");
text = getCharBlock(&tsize);
printf("Now input the pattern you seek to search for: \n");
pattern = getCharBlock(&psize);
x = findmatch(text, pattern, tsize, psize);
if(x == -1){
printf("No Match Found \n");
printf("No starting position for match exists \n");
}
else{
printf("Match Has Been Found! \n");
printf("Match starting position at index %d \n", x - 4);
printf("Remaining text after Match: <%s> \n", text + x );
printIt(text, x+psize, tsize);
}
free(text);
free(pattern);
}
char *getCharBlock(int *size){
char *input = (char*) malloc (80*sizeof(char) +1 );
if (input == NULL)
{
printf("No memory!\n");
exit(-1);
}
char a;
int i = 0;
a = getchar();
while( i<80 && a != '\n'){
if( ((a>= 'a') && (a <= 'z')) || ( (a>= 'A') && (a <= 'Z') ) ){
* (input + i) = a;
i++;
}
a = getchar();
}
* (input + i) = 0; // sg7! terminate the string
*size = i;
return input;
}
int next_state(char *text, char *pattern, char *m1, char *m2, int *index, int patternInd, int next_state, int advInd )
{
int state = 0;
if (text[*index] == pattern[patternInd]){
state = next_state;
printf( "%s\n", m1);
(*index)++;
}
else{
printf( "%s\n", m2);
if(advInd)
(*index)++;
}
return state;
}
int findmatch(char *text, char *pattern, int tsize, int psize) {
int index = 0;
int state = 0;
printf("Text=<%s> pattern=<%s> tsize=%d psize=%d \n",text, pattern, tsize, psize);
while (index <= tsize) {
switch (state)
{
case 0:
state = next_state(text,pattern, "test 1", "test1.1", &index, 0, 1, 1);
break;
case 1: // pattern[0] matched
state = next_state(text, pattern, "test 2", "test2.2", &index, 1, 2, 0);
break;
case 2: // pattern [0] [1] matched
state = next_state(text, pattern, "test 3", "test3.3", &index, 2, 3, 0);
break;
case 3: // pattern [0] [1] [2] matched
state = next_state(text, pattern, "test 4", "test4.4", &index, 3, 4, 0);
break;
case 4:
printf("DONE, index = %d \n",index);
return index;
break;
default:
printf("We should not be here! \n");
break;
} // case
} // while
return -1;
}
输出：
Please input a sequence of character text (characters only will be stored):
aaabcdef
Now input the pattern you seek to search for:
abcd
Text=<aaabcdef> pattern=<abcd> tsize=8 psize=4
test 1
test2.2
test 1
test2.2
test 1
test 2
test 3
test 4
DONE, index = 6
Match Has Been Found!
Match starting position at index 2
Remaining text after Match: <ef>
Please input a sequence of character text (characters only will be stored):
abcdefgh
Now input the pattern you seek to search for:
efgh
Text=<abcdefgh> pattern=<efgh> tsize=8 psize=4
test1.1
test1.1
test1.1
test1.1
test 1
test 2
test 3
test 4
DONE, index = 8
Match Has Been Found!
Match starting position at index 4
Remaining text after Match: <>
我希望它有所帮助。如果您有更多问题，请随时提出。
答案 1 :(得分：0)
我还没有阅读你的整个代码，我只关注你的无限循环问题。
findmatch（）函数中while循环的控制条件有问题。您正在检查psize＆lt; = tsize，但您永远不会更新任何这些变量。退出此循环的唯一其他情况是在最后一个返回-1的情况下，但是使用此代码，您永远不会到达那里（对于每种情况都有if / else情况，并且在情况下继续返回state = 0不匹配）。
你应该检查你的等待条件：
while (state != 4 && index < tsize)
此外，当您从findmatch（）获得返回代码时，应检查返回值为4以确保匹配。
如果您使用状态变量作为模式字符串的索引器，您还可以减少此函数中的大量if：
int findmatch(char *text, char *pattern, int tsize, int psize)
{
int i, state = 0;
for (i = 0; state < psize && i < tsize; i++)
{
if (text[i] != pattern[state])
{
// no match, reset state
i -= state;
state = 0;
}
else
// found a match, next state
state++;
}
if (state == psize)
return i - psize;
else
return -1;
}
希望它有所帮助！
答案 2 :(得分：0)
我在这看不到[x]。 可以通过数组指针访问数组。所以 state [0]是数组中的第一个char。你有状态== 0等等，状态== 3，这很好，但你必须在数组上工作。 我是菜鸟，但有类似的东西。 希望这会有所帮助。
答案 3 :(得分：0)
#include <stdio.h>
#include <stdlib.h>
int Myindex = 0;
char *getCharBlock(int *size);
int findmatchA(char *text, char *pattern, int tsize, int psize);
int findmatchB(char *text, char *pattern, int tsize, int psize);
int findmatchC(char *text, char *pattern, int tsize, int psize);
void printIt(char *ptr, int index, int size);
int main() {
char *text, *pattern, *text2, *pattern2, *text3,
*pattern3; // pointers for the characters you will read
char *p, *r; // some pointer variables
int tsize, psize, tsize2, psize2, tsize3, psize3, x, y, z; // some integers
printf(" \n");
printf("Please input a sequence of characters (only characters will be "
"stored ): \n");
text = getCharBlock(&tsize);
printf("\n");
// printf( "tsize is %d \n", tsize);
printf(" Now input the pattern you seek to search for: \n");
pattern = getCharBlock(&psize);
// printf( "tsize is %d \n", psize);
x = findmatchA(text, pattern, tsize, psize);
if (x == -1) {
printf("\n");
printf("No Match Found \n");
printf("\n");
printf("No starting position for match exists \n");
} else {
printf("\n");
printf("Match Has Been Found!!! \n");
// printf( "%d\n", x);
printf("\n");
printf("Match starting position at index %d \n", x - 3);
printf("\n");
printf("Remaining text after Match: \n");
printIt(text, x, tsize);
}
// //what should be passed?);
// looks for a match, returns -1 for failure or an int which is the index to
// the location where the match starts. the return values can be used to
// determine IF a match was found, and where.
printf("\n");
printf("Now input a sequence of character text for non-contiguous "
"matching(characters only will be stored): \n");
text2 = getCharBlock(&tsize2);
printf("\n");
printf(" Now input the pattern you seek to search for in a non-contiguous "
"manner: \n");
pattern2 = getCharBlock(&psize2);
y = findmatchB(text2, pattern2, tsize2, psize2);
if (y == -1) {
printf("\n");
printf("No match found \n");
printf("\n");
printf("No starting position for match exists \n");
} else {
printf("\n");
printf("Match has been found!!! \n");
printf("\n");
printf("Match starting position at index %d \n", y - 4);
printf("\n");
printf("Remaining text after match: \n");
printIt(text, y, tsize);
}
printf("\n");
printf("Now input a sequence of character text for multiple "
"matchings(characters only will be stored): \n");
text3 = getCharBlock(&tsize3);
printf("\n");
printf(" Now input the pattern you seek to search for: \n");
pattern3 = getCharBlock(&psize3);
z = findmatchC(text3, pattern3, tsize3, psize3);
printf("\n");
printf("The Number of Matches Is %d \n", z);
free(text);
free(pattern);
free(text2);
free(pattern2);
free(text3);
free(pattern3);
}
char *getCharBlock(int *size) {
// this would fill in the "string" of chars for the passed in char pointer.
char *input = (char *)malloc(80 * sizeof(char));
char a;
int i = 0;
a = getchar();
while (i < 80 && a != '\n') {
if ((a >= 'a' && a <= 'z') || (a >= 'A' && a <= 'Z')) {
*(input + i) = a;
i++;
}
a = getchar();
}
*(input + i) = '\0';
*size = i;
return input;
}
int findmatchA(char *text, char *pattern, int tsize, int psize) {
int index = 0;
int state = 0;
while (psize <= tsize) {
if ((*(text + index) == *pattern) && state == 0) {
state = 1;
index++;
// printf( "test 1 \n");
}
else if ((*(text + index) != *pattern) && state == 0) {
state = 0;
index++;
// printf( "test1.1 \n");
}
else if (*(text + index) == *(pattern + 1) && state == 1) {
state = 2;
index++;
// printf( "test 2 \n");
}
else if (*(text + index) != *(pattern + 1) && state == 1) {
state = 0;
index++;
// printf("test 2.2 \n");
}
else if (*(text + index) == *(pattern + 2) && state == 2) {
state = 3;
index++;
// printf("test 3 \n");
}
else if (*(text + index) != *(pattern + 2) && state == 2) {
state = 0;
index++;
// printf("test 3.3 \n");
}
else if (*(text + index) == *(pattern + 3) && state == 3) {
state = 4;
index++;
return index;
// printf("test 4 \n");
break;
}
else if (*(text + index) != *(pattern + 3) && state == 3) {
state = 0;
index++;
// printf("test 4.4 \n");
}
else {
return -1;
}
}
return index;
}
int findmatchB(char *text2, char *pattern2, int tsize2, int psize2) { // non-
//contiguous case
int index = 0;
int state = 0;
while (psize2 <= tsize2) {
if ((*(text2 + index) == *pattern2) && state == 0) {
state = 1;
index++;
// printf("test1\n");
}
else if ((*(text2 + index) != *pattern2) && state == 0) {
state = 0;
index++;
// printf("test1.1\n");
}
else if (*(text2 + index) == *(pattern2 + 1) && state == 1) {
state = 2;
index++;
// printf("test2\n");
}
else if (*(text2 + index) != *(pattern2 + 1) && state == 1) {
state = 1;
index++;
// printf("test2.2\n");
}
else if (*(text2 + index) == *(pattern2 + 2) && state == 2) {
state = 3;
index++;
// printf("test3\n");
}
else if (*(text2 + index) != *(pattern2 + 2) && state == 2) {
state = 2;
index++;
// printf("test3.3\n");
}
else if (*(text2 + index) == *(pattern2 + 3) && state == 3) {
state = 4;
index++;
// printf("test4\n");
break;
return index;
}
else if (*(text2 + index) != *(pattern2 + 3) && state == 3) {
state = 3;
index++;
// printf("test4.4\n");
}
else {
return -1;
}
}
return index;
}
int findmatchC(char *text3, char *pattern3, int tsize3, int psize3) {
int index = 0;
int pindex = 0;
int state = 0;
int matchcount = 0;
// printf( "tsize is %d \n", tsize3);
while (index <= tsize3) {
// printf( "test of inside loop \n");
// printf( "pindex is %d \n", pindex);
// printf( "tindex is %d \n", index);
// printf( " text value is %c \n", *(text3 + index));
// printf( " pattern value is %c \n", *(pattern3 + pindex));
if (*(text3 + index) == *(pattern3 + pindex) && state == 0) {
state = 1;
index++;
pindex++;
// printf( "test 1 \n");
}
else if (*(text3 + index) != *(pattern3 + pindex) && state == 0) {
state = 0;
index++;
// pindex++;
// printf( "test1.1 \n");
}
else if (*(text3 + index) == *(pattern3 + pindex) && state == 1) {
state = 2;
index++;
pindex++;
// printf( "test 2 \n");
}
else if (*(text3 + index) != *(pattern3 + pindex) && state == 1) {
state = 0;
index++;
// pindex++;
// printf("test 2.2 \n");
}
else if (*(text3 + index) == *(pattern3 + pindex) && state == 2) {
state = 3;
index++;
pindex++;
// printf("test 3 \n");
}
else if (*(text3 + index) != *(pattern3 + pindex) && state == 2) {
state = 0;
index++;
// pindex++;
// printf("test 3.3 \n");
}
else if (*(text3 + index) == *(pattern3 + pindex) && state == 3) {
state = 0;
index++;
pindex = 0;
matchcount++;
// printf("test 4 \n");
}
else if (*(text3 + index) != *(pattern3 + pindex) && state == 3) {
state = 0;
index++;
pindex = 0;
// printf("test 4.4 \n");
}
else {
return -1;
}
}
return matchcount;
}
void printIt(char *ptr, int index, int size) {
while (index < size) {
printf("%c", *(ptr + index));
index++;
}
printf("\n");
}