strlen()

Compute the length of a string

Synopsis:

#include <string.h>

size_t strlen( const char * s );

Arguments:

s
The string whose length you want to calculate.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The strlen() function computes the length of the string pointed to by s.

Returns:

The number of characters that precede the terminating null character.

Examples:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main( void )
  {
    printf( "%d\n", strlen( "Howdy" ) );
    printf( "%d\n", strlen( "Hello world\n" ) );
    printf( "%d\n", strlen( "" ) );

    return EXIT_SUCCESS;
  }

produces the output:

5
12
0

Environment variables:

LIBC_STRINGS
On 32-bit ARMv7 targets, you can use this environment variable to select the implementation for this function. The value is one of the following:
  • cortex_a9 — optimized for the ARM Cortex-A9 processor; assumes that no unaligned access is supported.
  • cortex_a9_aligned — optimized for ARM Cortex-A9; requires that unaligned memory access be enabled on the platform. If memory access is misaligned, this implementation falls back to the NEON version.
  • cortex_a9_neon — optimized for ARM Cortex-A9 using NEON.
  • generic — the default.
  • krait — optimized for the Qualcomm Krait CPU.
  • krait_neon — optimized for Qualcomm Krait using NEON.

Processes that register ISRs shouldn't use the NEON versions.

LD_PRELOAD
To use the implementation for this function that's optimized for ARM 64-bit architecture, you must set this environment variable. For example:
# export LD_PRELOAD=/lib/libstringsa64.so
            

Classification:

ANSI, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Read the Caveats
Signal handler Yes
Thread Yes

Caveats:

If you're using the implementation for this function that's optimized for ARM 64-bit architecture, it's unsafe to use it in an interrupt handler.