I want to create a program that checks if the input is syntactically valid in C -

how create c program takes in command in c input, , prints if there errors?

for example,

    input: for(i=0; i<5; i++);     no errors.      input: for((i=0); i>2,(i<5) ; i++);     no errors.      input: for(i=0, i<5; i++);     error.      input: for((i=0; i<5; i++));     error. 

i think shortest way compile input string, , check if errors occur. don't know how compile piece of code passed during runtime. also, there problem of undeclared variables.

c particuraly complicated parse. if remove pre-processor side of it, there still tricky parts.

if learning yourself, can c grammar (there in lex/yacc format ansi c) can at.

from example guess want able recognize subset of c, not entire language, correct? if case, should define subset , write parser it.

rather trying write parser hand, should learn grammars , parser generators if haven't worked them already.

if it's subset of c you're interested in, use peg parse generator packcc parser.

as super-simple example, following parser:

%prefix "mc"  stmt <- _ assign            { printf("assignment\n"); }         / _ if                 { printf("if\n"); }      / ( !eol . )* eol      { printf("error\n"); }  if <- 'if' _ '(' _ var _ ')' _ stmt   assign <- var _ '=' _ num _ ';' _ eol var    <- [a-za-z_] [0-9a-za-z_]* num    <- [0-9]+ _      <- [ \t]* eol    <- '\n' / '\r\n' / '\r'  %% int main() {     mc_context_t *ctx = mc_create(null);     while (mc_parse(ctx, null));     mc_destroy(ctx);     return 0; } 

will accept assignment (where lvalue variable name , rvalue integer) , if statements condition variable name. assuming parser in file mu.peg

home> packcc mu.peg home> gcc -o mu mu.c home> ./mu t = 5; assignment t = 5 error if (x) p = 3; assignment if if (x) if (y) t = 3; assignment if  if 

if, instead, need check sintatically valid c code @ runtime , there's compiler installed on system, tipically gcc or clang, can call via system() , intercept error. depending on type of checks want on code, can consider using static analyzer splint.

if need embed in application, can try tcc availble library.