Low level string manipulation functions in C

I'm working with a legacy program that does a bunch of markup manipulation, some of it higher-level and specific to the proprietary markup, some of it lower level string stuff.

I rewrote and documented the customized low level stuff (and used string.h stuff where applicable). I'm not not usually a C-coder, but I'm trying to learn.

• Am I duplicating core functionality of a standard library?

• Am I following conventions/best practices?

• Is the code efficient?

string_plus.h

/**
 * @file
 *
 * A small library of additional low level string manipulation functions. If any
 * functionality is duplicated from any of the normal libraries, it is due to
 * ignorance.
 */

#ifndef STRING_PLUS_H
#define STRING_PLUS_H

#include 

/**
 * Returns 1 if the front of @p text matches @p search_key, else 0.
 */
int begins_with(char const *text, char const *search_key);

/**
 * Condenses a string buffer by sliding all contents at @p p2 down to @p p1. In
 * other words, anything in between @p p1 and @p p2 is deleted. Returns @p p1.
 */
char *condense_buffer(char *p1, char *p2);

/**
 * Modifies @p text, removing all occurrences of @p c. Returns @p text.
 */
char *remove_char_occurrences(char *text, char const c);

/**
 * Inserts @p content into a buffer at @p p by shifting the buffer's data by @p
 * content's size. Returns a pointer at the end of the newly modified buffer.
 *
 * @warning Caller is responsible for guarding against a buffer overrun.
 */
char *insert_content(char *p, char const *content);

#endif /* Header load-once guard clause */

string_plus.c

```
#include "string_plus.h"

int begins_with(char const text, char const search_key) {
int result = 1;
while (search_key != '\0' && (result = search_key++ == *text++));
return result;
}

char condense_buffer(char p1, char *p2) {
while ((p2-1) != '\0') p1++ =*p2++;
return p1;
}

char remove_char_occurrences(char text, char const c) {
char *lead = text;
char *tail = text;
while (*lead != '\0

-
condense_buffer is equivalent to strcpy. If you still wish to implement it, use an idiomatic C construct:

while ((*p1++ = *p2++) != 0)
        {}

-
begins_with is equivalent to strncmp(text, key, strlen(key)). It might be argued though that strncmp approach requires a call to strlen and thus incurs performance penalty.

-
Do put the loop body on a separate line. Do not omit curly braces even for one-liners:

for (char *end = p + strlen(p); end >= p; end--) {
       *(end + content_len) = *end;
   }

StackExchange Code Review Q#107560, answer score: 2