How do I print everything before a specific word and everything after a specific word?

Question

I have a file called test.xml. What I am trying to do is print everything before the into a new file called. Then print my own custom <start>n n n</start>. Then print everything after the </start>

test.xml:

<more tests = 42 and more "34">

<start>10.213123 41.21231 23.15323</start>

<random stuff = "4">

<blah 234>

I tried using memcmp, doesn't seem to work.

// The main hub for generating new files with all the information in it.
void create_new_files(FILE *original, char *new_name, double x, double z,
                      double y, int val_pos, int incr_val, int max_val) {

    double i = 0;
    y = 10.1234;
    z = 30.231;

    FILE *generated_file = fopen(new_name, "r");

    // suppose to print everything before the <start>
    print_top_section(original);

    fprintf(generated_file, "<start>%lf %lf %lf</start>\n\n", i, z, y);

    // suppose to print everything after </start>
    print_bottom_section(original);

    fclose(generated_file);
}

// Prints the top section before it sees <start>
void print_top_section(FILE *original) {

    char line[MAX_LINE_LENGTH];
    while (memcmp(line, "<start>", sizeof("<start>")-1)) {

        fputs(line, stdout);
    }

}

// Prints the bottom section after it sees </start>
void print_bottom_section(FILE *original) {

    char line[MAX_LINE_LENGTH];
    while (memcmp(line, "</start>", sizeof("</start>")-1)) {

        fputs(line, stdout);
    }
}

Trying to make it so the output would be:

<this is a test = 1>

<more tests = 42 and more "34">

<start>0 10.1234 30.231</start> // This is my own custom line.

<random stuff = "4">

<blah 234>

Answer 1

Goal: Printing all data that is not in between <start> and </start>

You are using memcmp() to compare with a new declaration of char[].

char line[MAX_LINE_LENGTH];
while (memcmp(line, "<start>", sizeof("<start>")-1))

That wouldn't accomplish much. What are the contents of line?

So now, suppose your XML file looked as such:

CASE 1: 
ALONE LINE - NO TAGS

CASE 2:
<start>FOO</start>

CASE 3:
<start>
FOO
BAR
</start>

CASE 4: 
BEFORE <start> FOO  </start> AFTER

CASE 5: 
BEFORE <start>
FOO
BAR
</start> AFTER

• Case 1: Your line has no <start> or </start> tag
• Case 2: Your line has only <start> and </start>
• Case 3: Your <start> and </start> are alone on separate lines
• Case 4: Your <start> and </start> are on the same line but not alone
• Case 5: Your <start> and </start> are on separate lines but not alone

We need to make sure we get all data that is not in between <start> and </start>

Getting data before <start>

getline(&line, &len, fp)
char* start = strstr(line, "<start>")
int index = start - line; 
printf("%.*s", index, line);

Getting data after </start>

getline(&line, &len, fp)
char* end = strstr(line, "</start>")
int index = end - line + strlen("</start>"); 
printf("%s", line + index);

Here is a solution

FILE* fp = fopen("test.xml", "r");

// Set up for getline()
char* line;
size_t len;
ssize_t read;

bool enteredStart = false; // If we have entered into a <start>...</start> block
int index;
char* start; // Will be used to determine anything before <start>
char* end; // Will be used to determine anything after </start>

while ((read = getline(&line, &len, fp)) != -1) {
    // If the line contains both <start> and </start>
    if( ((start = strstr(line, "<start>")) != NULL) && ((end = strstr(line, "</start>")) != NULL) ) {   
        // Get the index where <start> exists and print everything before
        index = start - line; 
        printf("%.*s", index, line);

        // INSERT ANY CUSTOM INPUTS HERE

        // Get index where </start> has ended and print everything after
        index = end - line + strlen("</start>"); 
        printf("%s", line + index);

    }
    else if((start = strstr(line, "<start>")) != NULL) {
        // Get the index where <start> exists and print everything before
        index = start - line; 
        printf("%.*s", index, line);

        // We have entered <start> so we will stop printing until we encounter </start>
        enteredStart = true;

        // INSERT ANY CUSTOM INPUTS HERE
    }
    else if((end = strstr(line, "</start>")) != NULL) {
        // We have encounted </start> so we will start printing again
        enteredStart = false;

        // Get index where </start> has ended and print everything after
        index = end - line + strlen("</start>"); 
        printf("%s", line + index);
    }
    // If neither <start> nor </start> exist in the line 
    // and we are not in between <start> and </start> then we will print the line
    else if(!enteredStart) printf("%s", line);
}
fclose(fp);

Note: If you do not want to print blank lines or lines with just whitespace, you can trim the outputs yourself.