CODEWITHSUNDEEP
cc-strings
user13907
user13907

Reputation: 103

Modifying C strings in a loop, escaping characters

I am a bit new to C and I have to modify a program that I've been given. It outputs a string, but I have to modify that string making sure that it properly escapes CSV special characters. I'd know how to do that with Python, because it's a simple search-and-replace kind of thing, but I'm struggling with the strings in C.

Here is what I got so far:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void escape_csv(const char * src) {
    printf("Input: %s\n", src);
    
    char escapes[] = {',', '"', '\n', '\r', '\0'};
    int needs_quoting = !!src[strcspn(src, escapes)];

    char buf[strlen(src) * 2];

    int pos = 0;

    if (needs_quoting) {
        buf[pos] = '"';
        pos++;
    }
        

    for (int i = 0; i < strlen(src); i++)
    {
        if (src[i] == '"') {
            buf[pos] = '\"';
            pos++;
        }
        buf[pos] = src[i];
        pos++;
    }
    if (needs_quoting) {
        buf[pos] = '"';
        pos++;
    }
        
    printf("Output: %s\n", buf);
}

int main() {
    escape_csv("Test");
    escape_csv("Te\"st");
    escape_csv("Te,st");
}

It somehow works, but not quite. When I run it, it shows:

Input: Test
Output: Test
Input: Te"st
Output: "Te""st"�}(
Input: Te,st
Output: "Te,st

For some reason it's showing weird characters in the second example, and the last one is missing the final quote.

What am I doing wrong here? Is there another way to improve this, to simply get the escaped string at the end of the function?

Upvotes: 0

Views: 52

Answers (1)

Schwern
Schwern

Reputation: 165396

Strings in C are terminated with a null, '\0'. buf doesn't have one, so when you print it it will continue reading garbage until it happens to see a null byte.

Add a buf[pos] = '\0'; at the end of the algorithm.

Upvotes: 1

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