🧵 C <string.h> – String and Memory Manipulation Functions in C
🧲 Introduction – What Is <string.h> in C?
The <string.h> header provides a set of functions and macros for working with C-style strings and memory blocks. Strings in C are arrays of characters terminated by a null character ('\0'), and <string.h> gives you the tools to manipulate them—copying, comparing, concatenating, and more.
🎯 In this guide, you’ll learn:
- Common string and memory handling functions
- Syntax and examples for each
- Best practices and safety tips
- Real-world use cases
📦 Key Features of <string.h>
| Category | Functions |
|---|---|
| String length | strlen() |
| String copy/concat | strcpy(), strncpy(), strcat(), strncat() |
| String comparison | strcmp(), strncmp() |
| Memory operations | memcpy(), memset(), memcmp() |
| Search and tokenize | strchr(), strstr(), strtok() |
🔍 Commonly Used Functions
✅ strlen() – Get String Length
size_t len = strlen("hello"); // Returns 5
✅ strcpy() / strncpy() – Copy Strings
char dest[20];
strcpy(dest, "world"); // Copies the string
// or safer:
strncpy(dest, "world", 19); // Avoids buffer overflow
✅ strcat() / strncat() – Concatenate Strings
char str[20] = "Hello ";
strcat(str, "World!"); // Appends "World!" to str
✅ strcmp() / strncmp() – Compare Strings
if (strcmp("cat", "dog") < 0) {
printf("cat comes before dog\n");
}
📌 Returns 0 if strings are equal, a negative value if the first is less, positive if greater.
✅ strchr() / strstr() – Search in Strings
char *p = strchr("hello", 'e'); // Points to 'e'
char *s = strstr("abc123", "123"); // Points to "123"
✅ strtok() – Tokenize String
char str[] = "apple,banana,grape";
char *token = strtok(str, ",");
while (token != NULL) {
printf("%s\n", token);
token = strtok(NULL, ",");
}
📘 Useful for splitting input strings by a delimiter.
🧠 Memory Handling Functions
✅ memcpy() – Copy Raw Memory
memcpy(dest, src, size); // Fast block copy
✅ memset() – Set Memory
memset(arr, 0, sizeof(arr)); // Fill array with 0s
✅ memcmp() – Compare Memory Blocks
if (memcmp(buf1, buf2, size) == 0) {
printf("Buffers match");
}
📚 Real-World Use Cases
| Scenario | Function(s) Used |
|---|---|
| Parsing CSV/text | strtok(), strchr() |
| Copying strings | strcpy(), strncpy() |
| Comparing passwords/input | strcmp(), strncmp() |
| Allocating & clearing memory | memcpy(), memset() |
| Search in config strings | strstr(), strchr() |
💡 Best Practices & Tips
📘 Best Practice:
Use strncpy() instead of strcpy() to avoid buffer overflows.
💡 Tip:
Always make sure destination arrays are large enough before using string functions.
⚠️ Pitfall:strtok() modifies the original string—it is not thread-safe and should not be reused in nested loops.
📌 Summary – Recap & Next Steps
The <string.h> header is your go-to toolkit for low-level text processing and efficient memory operations. Mastering it is essential for building text-based applications, custom parsers, and binary data handlers.
🔍 Key Takeaways:
strlen(),strcpy(),strcat(),strcmp()are fundamental string tools- Use
memcpy(),memset(), andmemcmp()for raw memory operations strtok()is powerful for breaking strings into tokens- Be careful with buffer sizes and use
strncpy()/strncat()for safety
⚙️ Real-World Relevance:
Commonly used in text processing tools, file parsers, config readers, and data serialization/deserialization.
❓ Frequently Asked Questions (FAQ)
❓ What does <string.h> do?
✅ It provides functions for manipulating C strings (char arrays) and memory blocks.
❓ Is strcpy() safe?
⚠️ No. It doesn’t check for buffer overflows. Use strncpy() or ensure buffer size manually.
❓ Can I compare strings with ==?
❌ No. Use strcmp() for string comparisons in C. == compares memory addresses, not content.
❓ What’s the difference between memcpy() and strcpy()?
✅ memcpy() copies raw memory, including null bytes.strcpy() copies null-terminated strings only.
❓ How do I split a string in C?
✅ Use strtok():
char *token = strtok(input, ",");
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