Unexplainable change in C variable

Question

I've written a simple C program to convert char into Tokens. Things work fine but I'm unable to understand why the size variable value is changing.

typedef struct _token {
    int val;
} Token;

void parse( char* code, int size, Token** tokens ) {
    int i = 0;
    for (; i < size; i++) {
        tokens[i] = malloc(sizeof(Token));
        tokens[i]->val = code[i];  
    }
}

int execute( char *path ) {
    char* code;
    if ( read_file( path, &code ) != 0 ) {
        return -1;
    }
    int size = strlen(code) - 1;
    printf("BEFORE PARSE: %d\n", size);    // 1st printf
    Token *tokens;
    parse( code, size, &tokens );        
    printf("AFTER PARSE: %d\n", size);     // 2nd printf
    return 0;
}

if code contains "abcde", the output is:

BEFORE PARSE: 5
AFTER PARSE: 142786584

The second printf displays different values on different runs.

Please help !

PS: I'm a C noob !

EDIT:

int read_file(char* path, char** code) {
    FILE* fp = fopen ( path , "rb" );
    if( !fp ) {
        return -1;
    }

    fseek( fp , 0L , SEEK_END);
    long lSize = ftell( fp );
    rewind( fp );

    /* allocate memory for entire content */
    *code = calloc( 1, lSize+1 );
    if( !*code ) {
        fclose( fp );
        return -1;
    }

    /* copy the file into the buffer */
    if( 1 != fread( *code , lSize, 1 , fp) ) {
        fclose(fp);
        return -1;
    }

    fclose( fp );
    return 0;
}

Answer 1

You have a typical case of buffer overflow.

char* code;

Allocates a pointer to character (typically 8 bytes), not a buffer to hold your file data.

Same with

Token *tokens;

When you write to tokens in parse you overwrite part of your stack and size with it.

Allocate enough memory for them!

char * code = malloc(0x1000);
Token *tokens = malloc(0x100 * sizeof(Token *));

And pass the pointer, not it's address:

read_file( path, code );
parse( code, size, tokens );

Here is corrected code:

typedef struct _token {
    int val;
} Token;

void parse( char* code, int size, Token* tokens ) {
    int i = 0;
    for (; i < size; i++) {
            // you already have memory now
        tokens[i]->val = code[i];  
    }
}

int execute( char *path ) {
    char* code =  malloc(0x1000);
    if ( read_file( path, code ) != 0 ) {
        return -1;
    }
    int size = strlen(code) - 1;
    printf("BEFORE PARSE: %d\n", size);    // 1st printf
    Token *tokens = calloc(sizeof(Token), 0x100);
    parse( code, size, tokens );        
    printf("AFTER PARSE: %d\n", size);     // 2nd printf
    return 0;
}

Answer 2

It is because tokens is never initialized. Change it to:

Tokens **tokens = malloc(sizeof(Tokens *) * size);

Don't forget to free the memory when you are done with it:

for (; i < size; i++) {
    free(tokens[i]);
}

free(tokens);