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Diffstat (limited to '')
-rw-r--r-- | 1-24_syntax-checker.c | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/1-24_syntax-checker.c b/1-24_syntax-checker.c new file mode 100644 index 0000000..f56e4f7 --- /dev/null +++ b/1-24_syntax-checker.c @@ -0,0 +1,151 @@ +#include <stdio.h> + +/* The C Programming Language: 2nd Edition + * Exercise 1-24: + * "Write a program to check a C program for rudimentary syntax errors like + * unbalanced parentheses, brackets, and braces. Don't forget about quotes, both + * single and double, escape sequences, and comments. (This program is hard if + * you do it in full generality.)" + * + * Proksima from Freenode's ##c helped me understand full generality where + * Ixquick, Wikipedia, and StackOverflow all failed: a program that has full + * generality handles all use cases. In this case, my program should report no + * errors from a well formed C source file, and return correct errors for every + * non-valid C source file. + * + * I can tackle this one the same way I tackled the previous exercise: with a + * FSM. The trick is in catching the mismatched levels. + */ + +/* Create our nestable counts. These keep track of each type of syntax + * character. */ +#define PARENS 0 +#define BRACKETS 1 +#define BRACES 2 + +/* Create our states, which tell the parser what's going on. INSQ, INDQ, and + * INCM are much larger so it's easier to tell what's what. If I were better + * versed in binary operations, this could use less RAM. I intend to revisit + * this later on. */ +#define OUT 0 +#define INPR 1 +#define INBK 2 +#define INBC 3 +#define INSQ 100 +#define INDQ 1000 +#define INCM 10000 + +char c; +int counts[3]; +int state, i, linenr; + +int main() { + for (i = 0; i < 3; ++i) { + counts[i] = 0; + } + + state = OUT; + linenr = 1; + // Begin streaming! + while ((c = getchar()) != EOF) { + if (c == '\n') { + linenr += 1; + if (state >= INSQ) { + break; + } + } + if (c == '(') { + counts[PARENS] += 1; + state += INPR; + } + if (c == ')') { + counts[PARENS] -= 1; + state -= INPR; + if (counts[PARENS] < 0) { + break; + } + } + if (c == '[') { + counts[BRACKETS] += 1; + state += INBK; + } + if (c == ']') { + counts[BRACKETS] -= 1; + state -= INBK; + if (counts[BRACKETS] < 0) { + break; + } + } + if (c == '{') { + counts[BRACES] += 1; + state += INBC; + } + if (c == '}') { + counts[BRACES] -= 1; + state -= INBC; + if (counts[BRACES] < 0) { + break; + } + } + if (c == '"' && state > INDQ) { + state -= INDQ; + if (state < 0) { + break; + } + } + if (c == '"' && state < INSQ) { + state += INDQ; + if (state >= (INDQ * 2)) { + break; + } + } + if (c == '\'' && state > INSQ && state < INDQ) { + state -= INSQ; + if (state < 0) { + break; + } + } + if (c == '\'' && state < INSQ) { + state += INSQ; + if (state >= (INSQ * 2)) { + break; + } + } + } + + if (state != 0) { + printf("SYNTAX ERROR: "); + + if (state >= INSQ && state < INDQ) { + printf("Unclosed single quote on line %d!\n", linenr); + return 1; + } + if (counts[PARENS] > 0) { + printf("Unclosed parenthesis on line %d!\n", linenr); + return 1; + } + if (counts[PARENS] < 0) { + printf("Too many close parentheses on line %d!\n", linenr); + return 1; + } + if (counts[BRACKETS] > 0) { + printf("Unclosed brackets on line %d!\n", linenr); + return 1; + } + if (counts[BRACKETS] < 0) { + printf("Too many close brackets on line %d!\n", linenr); + return 1; + } + if (counts[BRACES] > 0) { + printf("Unclosed braces on line %d!\n", linenr); + return 1; + } + if (counts[BRACES] < 0) { + printf("Too many close braces on line %d!\n", linenr); + return 1; + } + } + + printf("All clean.\n"); + return 0; +} |