Remove certain characters from char*

Question

I've got an array of char* with serial data that I'm trying to remove ':' from. I have tried to iterate through the char*, find and remove any colons but it just comes out as garbage.

 char* espData[15];
 // pull data from serial and tokenize with strtok > feed to espData
 for(int x = 0; x < index-1; x++){
 size_t nullTerm = strlen(espData[x]);
 espData[x][nullTerm - 1] = '0円';
 char* output
 for(size_t i = 0; i < strlen(espData[x]); ++i){
 if(espData[x][i] != ':') output += espData[x][i];
 }
 espData[x] = output;
 Serial.println(espData[x]);
 }

Moving the null character works fine (I wanted to get rid of the last character in every string). Most of the answers I found for general C++ used std::string which we don't have access to.

• Ignacio Vazquez-Abrams: Arithmetic on a char* does nothing to its contents.
• Jaromanda X: the comment tokenize with strtok suggests your code uses strtok, which would be one (probably bloated) solution - yet your code doesn't use strtok!!?
• Jaromanda X: espData[x][nullTerm - 1] = '0円'; is redundant code
• John Burger: @Jaromanda Actually, it overwrites the last character in the string - or underflows the buffer if nullTerm is 0!
• Jaromanda X: @JohnBurger - of course you're right

Answer 1

You've assumed that a char * is some kind of string object, since you've got the following line of code: output += espData[x][i];, and then later espData[x] = output;

It quite simply doesn't work like that. At best you can point output inside espData[x] and then do some other logic: but your attempt to "accumulate" the correct characters is incorrect.

Please consider the following code instead:

char* espData[15];
for(int x = 0; x < index-1; x++){
 size_t nullTerm = strlen(espData[x]); // Get current length
 char* output = espData[x]; // Start of string
 for (size_t i = 0; i < nullTerm; ++i){
 if(espData[x][i] != ':') { // If it's NOT a colon
 *output++ = espData[x][i]; // Copy character 'up'
 } // if
 // If it WAS a colon, then
 // output does NOT get incremented
 } // for
 *output = '0円'; // End string off with NUL
 Serial.println(espData[x]);
} // for

• Tri42: That works perfectly, thank you! I have never been great with pointers
• John Burger: @Tri42 I just finished a pointer-post on another question. Take a look: arduino.stackexchange.com/a/25317/22924