Memory modification when using strtol() and atoi() functions

Question

I have the code (simplified a little for example)

char *op = CURRENT_PARSED_STRING.operand;
if(op){
    printf("%s\n", op);
    char q[] = "12h";
    int a = atoi(q);
    printf("%d %s\n", a, op);
}

CURRENT_PARSED_STRING is an instance of a structure that looks like this

typedef struct ASSEMBLY_LINE{
    char *marker;
    char *operator;
    char *operand;
    char *comment;
} ASSEMBLY_LINE;

when executing the line

int a = atoi(q);

CURRENT_PARSED_STRING.operand changes, and with it the op. In this case, the correct value is written in a. Here is the result of the execution:

12h    //op content before
12 Q4R //correct value and garbage

Changing atoi() to strtol() does not work. This code is needed to illustrate the problem, in fact, I need to convert to a number exactly op.

Edit: yes, I made a mistake with the format specifier, but that was not the reason. I checked my program in the debugger, and it showed that CURRENT_PARSED_STRING is completely fine, right up to the line with atoi. I included all the flags when compiling, but that didn't work either. I don't really understand how to make the question cleaner because CURRENT_PARSED_STRING appears in different parts of the code and for full reproducibility I would have to attach almost all the code. But I see that the structure looks intact - the lines end with a null character, unused fields = NULL.

Answer 1

The problem is most likely an incorrect format string. The variable a is an int so you want to use the format %d (%ld is for long):

printf("%d %s\n", a, op);