comparing strings when 1 string contains part of the other string

Question

I am using the following code to compare packetbuffer to a string,

char packetBuffer[UDP_TX_PACKET_MAX_SIZE];
!strcmp(packetBuffer, "turn on light")

however how could I use to compare it to a string should packetbuffer = testing1234 and the string to be compared to equal "testing", with out the last 4 digits?

Answer 1

The function you are looking for is strstr :

if (strstr(packetBuffer, "testing") != NULL)
{
    // packetBuffer contains "testing"
    // so do something...
}

Note: if you need to test for the substring just at the start of the string then you can do it like this:

if (strstr(packetBuffer, "testing") == packetBuffer)
{
    // packetBuffer starts with "testing"
    // so do something...
}

Answer 2

If you can use standard C library, strncmp is useful.
The length is also checked to make sure there are exactly 4 characters (not just digits) after "testing".

if (strlen(packetBuffer) == 11 && strncmp(packetBuffer, "testing", 7) == 0) {
    // they are equal
}

Note that this is not very good code since some magic numbers are used.