C - Remove/Replace Characters in a String

When I needed to remove/replace characters in a string, I posted a question here on stackoverflow.

I have used the strstr function in a loop, but was looking for a simpler solution. A C implementation equivalent to the C# String.Replace method might work.

 Problem

• Given a string (example : captured by LoadRunner's web_reg_save_param).
• Replace all the & character sequences with the & character.

 Solution #1

Simple Solution

char strSource[] = "/url/i.jsp?id=10002&c=10008&p=AC&v=2&s=3&m=1";
char strTemp[1024];
char *s = (char*)strSource;
int i=0;

while (*s)
{
    strTemp[i++] = *s;
    if (strncmp(s,"&",5) == 0)
    {
        s += 5;
    }
    else
        s++;
}
strTemp[i] = 0;

// strTemp = /url/i.jsp?id=10002&c=10008&p=AC&v=2&s=3&m=1

This works for this specific problem, but what if we want to be more flexible?

 Solution #2

• Create a reusable function.
• Pass the source, from and to strings as parameters to the function.
• Dynamically determine the length of the strings.
• Save the resulting string into a LoadRunner parameter.

Flexible Solution

void solution2 (char *strSource, char *strFrom, char *strTo, char *strParam)
{
	char strTemp[1024];
	char *s = (char*)strSource;
	int i=0;
	int iLenFrom = strlen (strFrom);
	int iLenTo   = strlen (strTo  );

	while (*s)
	{
		if (strncmp (s, strFrom, iLenFrom) == 0)
		{
			strncpy (&(strTemp[i]), strTo, iLenTo);
			i += iLenTo;
			s += iLenFrom;
		}
		else
		{
			strTemp[i++] = *s;
			s++;
		}
	}
	strTemp[i] = 0;

	lr_save_string (strTemp, strParam);
}

Action()
{
	char strSource[] = "/url/i.jsp?id=10002&c=10008&p=AC&v=2&s=3&m=1";

	lr_save_string (strSource, "pNewValue0");

	solution_2 (strSource, "&",   "&",     "pNewValue1");
	solution_2 (strSource, "&",   "[AAA]", "pNewValue2");
	solution_2 (strSource, "&aaamp;", "[BBB]", "pNewValue3");
	solution_2 (strSource, "&",   "",      "pNewValue4");
	solution_2 (strSource, "00",      "[X]",   "pNewValue5");

	// Parameters created

	// pNewValue0 = /url/i.jsp?id=10002&c=10008&p=AC&v=2&s=3&m=1
	// pNewValue1 = /url/i.jsp?id=10002&c=10008&p=AC&v=2&s=3&m=1
	// pNewValue2 = /url/i.jsp?id=10002[AAA]c=10008[AAA]p=AC[AAA]v=2[AAA]s=3[AAA]m=1
	// pNewValue3 = /url/i.jsp?id=10002&c=10008&p=AC&v=2&s=3&m=1
	// pNewValue4 = /url/i.jsp?id=10002c=10008p=ACv=2s=3m=1
	// pNewValue5 = /url/i.jsp?id=1[X]02&c=1[X]08&p=AC&v=2&s=3&m=1

	return 0;
}

 Moving Forward

• Dynamically allocate the strTemp variable.
• Error checking for empty strings and chars not found.
• Replace strncmp/strncpy with memcmp/memcpy.